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21.09.2017  
  


Achievements


MAIN ACHIEVEMENTS 2015

MAIN ACHIEVEMENTS 2015

Theme № 8.1. Electron Phenomena and Quantum Transport in Strongly-Correlated Metallic, Semiconducting and Hybrid Systems

Section II. “Physical sciences”, subsection 8. “Actual problems of condensed matter physics including quantum macrophycics, mezoscopy, nanostructure physics, spintronics, superconductivity”.
Programs of fundamental scientific researches for state academies of sciences in years 2013-2020

Realization of Superconducting Qubits and the Advantages of Josephson Pi-Junctions Using in Their Structure
(together with MISiS, Russian Quantum Center, MIPT and Karlsruhe Institute of Technology, Germany)

In 2015 the first Russian superconducting qubit was realized and its properties were studied.

Figure 1. Qubit microphotography and its spectrum

The superconducting flux qubit with integrated inverter of superconducting phase (a pi-junction developed in ISSP RAS [1]) was also fabricated. The pi-junction allows to reach qubit operation mode without external magnetic field needed in conventional case that provides increase of the qubit coherence time and makes multi-qubit architecture more compact.

Figure 2. The system of two qubits connected with one microwave resonator. The left qubit contains a pi-junction and its operating (black) points shifted by half of magnetic flux quantum compared with operating (red) points of a conventional qubit (one of them corresponds to the absence of an applied magnetic field).

[1] A.V. Shcherbakova et al. Supercond. Sci. Technol. 28, 025009 (2015).

Evidence on the Macroscopic Length Scale Spin Coherence for the Edge Currents in a Narrow HgTe Quantum Well
Currents in a Narrow HgTe Quantum Well

Spin-polarized electron transport is experimentally investigated between two ferromagnetic contacts, placed at the edge of a two-dimensional electron system with band inversion. The system is realized in a narrow (8 nm) HgTe quantum well, the ferromagnetic side contacts are formed from a pre-magnetized permalloy film. In zero magnetic field, a significant edge current contribution is detected to the transport between two ferromagnetic contacts. This transport is shown to be sensitive to the mutual orientation of the magnetization directions of two 200 μm-spaced ferromagnetic leads. This is a first direct experimental evidence on the spin-coherent edge transport over the macroscopic distances. Thus, the spin is extremely robust at the edge of a two-dimensional electron system with band inversion, confirming the helical spin-resolved nature of edge currents. (JETP LETTERS, , vol. 101, 814 (2015))

The First Observation of the Magnetoresistance "Slow Oscillations" along Conducting Layers in Layered Crystals.

Magnetoresistance slow oscillations along conducting layers in quasi-two-dimensional single crystals of TbTe3 and GdTe3 rare-earth tellurides were observed for the first time. Oscillation period is not determined by the section of any pocket in a Fermi surface that follows from a very weak temperature dependence of their amplitude but it is connected with the presence of two close in frequency Shubnikov-de Haas oscillations because of a finite interlayer transfer integral tz. From the experimental data we have obtained the estimate for the integral tz ≈ 1meV in these crystals; it is difficult to be obtained by other methods. (P.D. Grigoriev, A.A. Sinchenko, P. Lejay, O. Leynaud, V.N. Zverev, and P. Monceau, “Slow oscillations of in-plane magnetoresistance in strongly anisotropic quasi-two-dimensional rare-earth tritellurides”, http://arxiv.org/abs/1504.06064)

Figure 1. Fast and slow oscillations of magnetoresistance on the GdTe3 sample at T=4.2 K. The insert on the right image shows Fourier oscillations spectrum.

Domain Structure under Microwave Radiation

On the samples of GaAs/AlGaAs heterostructures with two-dimensional electron systems in the induced by microwave radiation state with suppressed dissipation the studies of earlier detected domain structure irregular restructuring over time occurring without visual external impacts were carried out. It was established that the effect mainly consists in spontaneous electric field domain overturn. Consequently the signal of the microwave photo-emf changes its sign (Fig. 1(a)), and the dependences of photo-emf extremes on various parameters are symmetrical towards some value that can be close to zero (Fig. 1(b)). Such a polarization inversion effect is undoubtedly connected with spontaneous symmetry breaking and it assumes the existence of heretofore unknown sample response mechanism to spontaneous electric field. It was detected that domain structure restructuring can occur in the form of series of periodic self-oscillations with irregular extinctions (Fig. 2)

(Phys. Rev. Lett. (2015), 114, 176808,  JETP Letters (2015),102, 101)

Figure 1. (a) The dependence of microwave photo-EMF on the signal time. (b) The dependence of minimal and maximal photo-EMF values on radiation frequency.

Figure 2. Photo-EMF signals from three different sample contacts.

Theme № 8.2. Interparticle Interactions and Collective Phenomena in Electron and Exciton Systems in Semiconducting Nanoctructures

Section II. “Physical sciences”, subsection 8. “Actual problems of condensed matter physics including quantum macrophycics, mezoscopy, nanostructure physics, spintronics, superconductivity”.
Programs of fundamental scientific researches for state academies of sciences in years 2013-2020

Detection of a Novel Weakly Damped Plasma Mode of Plasma Oscillations in a Gated Two-Dimensional Electron System.

In the two-dimensional electron system with conductivity exceeding speed of light a novel plasma oscillation relativistic mode weakly damped down to room temperatures was detected. The necessary conditions for its existence are high conductivity and the presence of a close metal gate that indicates polariton nature of the detected mode. It was found that the mode has abnormal small width of the resonance absorption line; it is noticeably less than the width expected from the time of impulse relaxation for two-dimensional electrons. The relativistic plasma mode properties open up great possibilities for fabrication of fast detectors and subterahertz radiation generators necessary for the development of modern telecommunication equipment.

Figure 1. The experiment scheme (a), a novel plasma mode with abnormal small width of 0.4 GHz (b), the dependence of mode frequency on electron system conductivity, (c) temperature impact on plasma mode damping.

V.M. Muravev, P.A. Gusikhin, I.V. Andreev, I. V. Kukushkin “Novel Relativistic Plasma Excitations in a Gated Two-Dimensional Electron System” Phys. Rev. Lett., 114, 106805 (2015)

Theme № 8.3. Self-Organization of Nanostructured Systems and Defect Physics in Semiconductors and Dielectrics

Section II. “Physical sciences”, subsection 8. “Actual problems of condensed matter physics including quantum macrophycics, mezoscopy, nanostructure physics, spintronics, superconductivity”.
Programs of fundamental scientific researches for state academies of sciences in years 2013-2020

Homogeneous coating of a trilayer graphene was synthesized and studied by scanning tunneling microscopy and photoelectron spectroscopy on the technologically relevant vicinal substrate SiC(001)/Si(001). The coating contains nanodomains having one preferred direction in interdomain boundaries. Low-temperature transport measurements demonstrate that the self-aligned nanodomain structure can induce a charge transport gap opening at temperatures below 100 K. The charge transport gap allows achieving big current on-off ratios (~104) in an ABA-stacked trilayer graphene. The results show the feasibility of creating new electronic nanostructures using graphene on cubic silicon carbide surface.

Figure 1. (a) STM image of the vicinal SiC(001). The step direction is close to the direction [110] of the SiC crystal lattice. (b-d) STM images of a trilayer graphene synthesized on the vicinal SiC(001). The lattices in adjacent nanodomains are rotated 17° clockwise (GrR) and 10° counterclockwise (GrL) relative the nanodomain boundary (NB). (e) Schematic model of the NB for the asymmetrically rotated domains in panels (c) and (d). (f) Schematic drawing of nanocontacts during transport measurements. (g, h) Volt-ampere characteristics changed at 300, 250, 200, 150, 100, 50 and 10 K. Current was directed transversely to nanodomain boundaries during the measurements. (i) Corresponding dI/dV curves for temperatures below 150 K. (ACS Nano (2015), 9, 8967-8975)

Reactions in SOFC Electrodes

Joint use of Raman spectroscopy (RS) and impedance spectroscopy methods combined with principally new geometry of SOFC samples fabricated on the basis of optically transparent single-crystalline membranes of solid electrolyte allowed the in-situ study of SOFC composite electrode reaction kinetics under the working conditions in a wide temperature range. The carried out analysis within Avrami-Erofeev model (Fig. 1) of results obtained combined with the results of thermogravimetric analysis (TGA) testifies in favour of the course of redox reactions on the contact of ion conductor YSZ with electronic conductor (Ni) through the formation of NiO nickel oxide nanograins.

Figure 1. The curves of NiO reduction in the SOFC composite anode measured by RS and TGA in Avrami coordinates

Radiation Stability of Organic Polymers

Considerable increase in radiation stability of organic polymers at the formation of their composites with inorganic nanoparticles explained by fast recovery of broken by irradiation interatomic bonds at fixed by nanoparticles molecules was set (see Figure). On the other hand, reversible plasticization of such composites by X-ray radiation was detected for the first time; it can be explained by injection to polymers from electron excitation nanoparticles formed in them by gamma-quantum absorption.

Figure: The effect of ultraviolet radiation on the deformation curves of pure polystyrene and its composite having nanoparticles. Softening caused by irradiation is much stronger in pure polystyrene (the upper curve) than in the composite and composite stability recovery after the end of irradiation happens much faster.

Theme № 8.4. Phase Transitions, Structure (Atomic, Magnetic, Defect) and Properties of Crystals, Disordered and Composition Micro- and Nanosystems at Standard and High Pressure

Section II. “Physical sciences”, subsection 8. “Actual problems of condensed matter physics including quantum macrophycics, mezoscopy, nanostructure physics, spintronics, superconductivity”.
Programs of fundamental scientific researches for state academies of sciences in years 2013-2020

Design of Nanocrystalline Materials Structure

The principles of design for nanostructure forming at light amorphous alloy crystallization under the influence of heat treatment and deformation were developed. The conditions providing maximum number of potential nucleation sited for the nanocrystals as well as the formation of the nanostructures with optimal nanocrystal size and volume fraction of the nanocrystalline phase leading to an increase in strength properties were determined. When combined deformation and heat treatment processing, the formation of nanocrystals (Fig. 1) occurs in the shear bands areas (Fig. 2). The amorphous-nanocrystalline samples Al-Ni-Gd exhibit the near-record (1.6 GPa) for light alloys strengths (1.5 GPa, Fig. 3). (Adv. Res. Mater. Sci., 2016, accepted for publication)


Figure 1.Nanocrystals formed at deformation

Figure 2. Shear band network

Figure 3. Dependence of Al87Ni8Gd5 alloy microhardness on deformation (at pressure torsion)
(при вращении под давлением)

Precursor of Nitrogen Polymerization in Cesium Azide

CsN3 cesium azide was analyzed by Raman spectroscopy at room temperature and pressures up to 30 GPa for the first time. Transitions to phase III (at 0.5 GPa), phase IV (at 4.3 GPa) and phase V (at 19 GPa) occur sequentially at pressure increase. Weak peak produced by anion bending oscillations (Fig. 1a detected for phase V at 27.5 GPa) indicates covalent bond formation and probable beginning of nitrogen polymerization predicted theoretically. Inorganic azides are interesting as precursors for synthesis of new nitrogen polymer forms and also in view of their possible industrial application as initiating explosives and the sources of chemically pure nitrogen. (S.A. Medvedev, O.I. Barkalov, P. Naumov, T. Palasyuk, J. Evers, T.M. Klapötke, C. Felser. J. Appl. Phys. 117 (2015) 165901)

Figure 1. Characteristic spectrums of CsN3 Raman scattering within the range of lattice vibration frequencies (a) and in the area of valence vibrations (b) at different pressures.

Figure 2. The dependencies of Raman active mode frequencies on pressure. The vertical dash lines show the phase stability boundaries.

Theme № 9.1. Heat-Resistant Materials for New Equipment.

Section II. “Physical sciences”, subsection 9. “Material physics: new materials and structures including fullerenes, nanotubes, graphenes, other nanomaterials, and also metamaterials (in the fields of physics and technologies of new functional materials for effective power conversion”.
Programs of fundamental scientific researches for state academies of sciences in years 2013-2020

Diamagnetic oxides can, under certain conditions, become ferromagnetic at room temperature and therefore are promising candidates for future material in spintronic devices. Contrary to early predictions, doping ZnO with uniformly distributed magnetic ions is not essential to obtain ferromagnetic samples. Instead, the nanostructure seems to play the key role, as room temperature ferromagnetism was also found in nanograined, undoped ZnO. Obtained experimental evidences and developed theoretical model indicate that diamagnetic zinc oxide can acquire ferromagnetic properties (even at room temperature and without doping) if zinc oxide is polycrystalline and the size of the grains is small enough. By low energy muon spin relaxation (μSR), transmission electron microscopy and magnetic measurements it was shown that volume fraction of zinc oxide nanocrystalline film possessing ferromagnetic properties is proportional to the fraction of volume occupied by grain boundaries. By molecular dynamics method and density functional theory it was shown that ferromagnetically coupled electron states exist in grain boundaries of undoped ZnO. (Scientific Reports 5 (2015) 8871)

Averaged zero field μSR asymmetry, normalized to the initial detector asymmetry, for the single crystal (black dots), the coarse grained (blue dots), and the fine grained (red dots) ZnO sample. Plotted is the normalized detector asymmetry; the relaxing amplitude of the asymmetry is a measure for the magnetic volume fraction. The strongest relaxation is found for the fine grained sample (red dots), corresponding to a total magnetic volume fraction of about 35%. For the coarse grained sample (blue dots), the magnetic volume fraction is approx. 15%. The non–magnetic ZnO single crystal reference (black dots) shows no significant magnetic volume fraction.

By directional crystallization from melt we have obtained Al2O3-Y3(Er3)Al5O12, Al2O3-GdAlO3 and Al2O3-ZrO2(Y2O3) profiled oxide eutectics possessing high creep resistance, wear resistance, corrosion resistance, high chemical inertness, strength and thermo-oxidative resistance at the temperatures of 1400-1600°С. Unique combination of oxide eutectics properties along with the possibility of obtaining of profiled blanks close in their geometry to final product shape provides broad prospects for their use as turboshaft engines components for the increase of operating temperatures leading to considerable efficiency improvements in many constructions.

At the top: profiled oxide eutectics. At the bottom: the microstructure of profiled eutectics: a) Al2O3-Y3Al5O12, b) Al2O3-GdAlO3 (fiber diameter of GdAlO3 is 450 nm, c) Al2O3-ZrO2(Y3Al5O12).

Novel High-Temperature Composites with Oxide Matrix

High-temperature composites with oxide matrix and molybdenum fibres were obtained for the first time; their crack resistance is comparable with high-strength metal alloy crack resistance, the stress-strain curves of composites are quasi-plastic. Addition of molybdate-forming elements to the matrix enhances oxidation resistance of these composites. Long high-temperature exposures of composites do not reduce essentially their strength both at room and high temperatures. The composites obtained can be a basis for effective heat resistant, refractory and crack resistant materials; their usage in gas turbines will considerably enhance their efficiency.

Theme № 9.2. Novel Functional Materials for Microelectronics, Optoelectronics and Effective Power Conversion.

Section II. “Physical sciences”, subsection 9. “Material physics: new materials and structures including fullerenes, nanotubes, graphenes, other nanomaterials, and also metamaterials (in the fields of physics and technologies of new functional materials for effective power conversion”.
Programs of fundamental scientific researches for state academies of sciences in years 2013-2020

Novel Materials for Visible Spectrum Radiation Source

1). New data on luminescent properties of GaSe- (Fig. 1) and GaTe-based 2D structures with thickness up to single cell was obtained; optical stability of these materials perspective for developing of new visible spectrum light-emitting devices was studied.

Figure 1. a). GaSe 2D structure with thickness of single cell (AFM). b). The results of this foil thickness measurement along the black line on (a).

2) Light-emitting junctions in Eu, Tb and Tm ions at Gd2(MoO4)3 matrix combined doping were studied; it allowed to proceed to developing of materials for construction of new economical visible spectrum light sources based on cheaper lithium-borate glass (LBG) matrix. Figure 2 shows the samples photographed at luminescence optical excitation at wavelength λe=365 nm. Obtaining of photochromic luminescent glasses changing their color under UV radiation (Fig. 3) and possessing complete and instantaneous color reversibility is the important result.

Figure 2. Luminescent LBG samples ( le=365 nm).

Figure 3. Photochromic luminescent glass color at UV radiation relative intensity of 25, 50 and 100 % (from left to right).

1. O. Del Pozo-Zamudio, S. Schwarz, M. Sich, A. Akimov, M. Bayer, R.C. Schofield, E.A. Chekhovich, B.J. Robinson, N.D. Kay, O. Kolosov, A.I. Dmitriev, G.V. Lashkarev, D.N. Borisenko, N.N. Kolesnikov, A.I. Tartakovskii. Photoluminescence of two-dimensional GaTe and GaSe films. 2D Materials, 2015, v. 2, 035010.

2. V.V. Sinitsyn, B.S. Redkin, A.P. Kiselev, S.Z. Shmurak, N.N. Kolesnikov, V.V. Kveder, E.G. Ponyatovsky. "White" phosphor on the basis of Gd2(MoO4)3:Eu,Tb,Tm single crystal. Solid State Sciences, 2015, v. 46, p. 80-83.

Spherical Microparticle Shaped Photonic Crystals

Spherical shaped microparticles with a size from 5 to 20 µm formed by SiO2 monodisperse colloidal particles by their close-packing in a face-centered cubic lattice analogously to opal-like structures were synthesized. The synthesis was conducted by spray drying of silicone dioxide colloidal particles aqueous suspension in the air at room temperature not using surfactant. Such particles having controllable sizes and given pore system, special structure and morphology are perspective for application in photonics, biological and chemical sensors, catalysis, pharmacology, etc.

STM image of the microparticle with a diameter of 30 µm formed from SiO2 colloidal particles with a diameter of 430 nm and reflectance spectrum of the particles formed by colloidal particles with a diameter of 200 nm (λ2) and 430 nm (λ41).

А.А. Zhokhov, V.М. Masalov, N.S. Sukhinina, D.V. Matveev, P.V. Dolganov, V.K. Dolganov, G.A. Emelchenko, Photonic crystal microspheres, Optical Materials, 49 (2015) 208-212

Theme № 12.1. Nonlinear Processes in Nanocomposite Magnetic Films, Liquid-Crystal Materials, on the Surface and in the Volume of Quantum Liquid.

Section II. “Physical sciences”, subsection12. “Modern problems in radiophysics and acoustics including fundamental principles of radiophysical and acoustic methods of communication, location and diagnostics, study of nonlinear wave effects”.
Programs of fundamental scientific researches for state academies of sciences in years 2013-2020

Critical Effect of NiFe Thin Film Shape on Its Properties.

The effect of the shape and the edges of Ni81Fe19 low-dimensional structured magnetic films (30 nm) (Fig. 1) on their magnetization switching processes was studied. Kinetics of transformation processes for the domain structure of the strips having width of 30, 10 and 3 µm (A, B, C on Fig. 1) was recorded using magnetooptical indicator film technique. It was shown experimentally and by micromagnetic modeling (Fig. 2) that magnetostatic fields forming on strip edges close to their intersections are key in forming of inhomogeneous distribution of switching spins and modes in thin soft magnetic films. In particular, in this way in the strips parallel to the applied field along their sides coupled pairs of spin vortices are forming. Inverse proportion of their initiation HCR critical fields to b strip width was detected (Fig. 3). It was established that HCR also depends on d size (1-5 on Fig. 1) of the structures external towards the studied ones. The obtained results are important for spintronics element developing (accepted for publishing to JMMM).

 

Density of Photonic States in Cholesteric Liquid Crystals

The method for determination of density of photonic states in a cholesteric liquid crystal with a photonic band in visible wavelength ranges was offered and realized. The method is based on the connection of differences in refractive indexes for circularly polarized waves with rotation of the plane of polarization of light by photonic structure. A comparison of the experiment with calculations has shown that the group velocity of light, vg, in the center of the forbidden photonic band for a sample of finite thickness, d, exceeds the velocity of light in vacuum, c (vg≈2.05 s). Maxima of density of photonic states determine wave lengths of laser generation in a photonic structure.

Density of photonic states in a cholesteric photonic crystal (the solid line), normalized to density of states in the structure without photonic band ρ0. The dashed line shows the calculated density of photonic states. Two vertical lines show the edges of the forbidden photonic band. d=5.8 µm. (Phys. Rev. E 91, 042509 (2015)).

Vortex Motions Forming by Waves on Water Surface.

New mechanism for vorticity generation by the waves on water surface has been observed for the first time. It was experimentally established that the generation of vortex flow is not the peculiarity of Faraday waves: the vortices appear in a square cell and a cylindrical cell with broken symmetry at excitation amplitudes below the Faraday instability threshold. It was shown that formation of vortex flow caused by the interaction between propagating surface waves with noncollinear wavevectors. (JETP Letters (2015), 102, 486-490)


Figure 1. Scheme of the experimental setup

Figure 2. Vorticity generated by the standing surface waves.

The scheme of the experimental setup is shown on fig. 1. A square vessel (5) filled with water was attached to the platform (6) that performed harmonic oscillation in a vertical direction. The amplitude and the frequency of platform vibrations were specified by an external generator. To visualize the surface flow hollow glass microspheres (3) were added into the water. Photocamera (2) took sequential pictures of the water surface illuminated by the flash (1).

Fig. 2 shows vorticity on water surface in a square cell in the result of the interaction between standing waves excited by vertical oscillation of the platform at the frequency of 45.5Hz and acceleration 0.44g. Regions of red and blue color have the vorticity of an opposite sign. The absolute value of vorticity grows with the increase of wave amplitude.

The theoretical model of the observed phenomenon was built by ITF RAS researchers. Theory and experimental results are in good agreement.

 

MAIN ACHIEVEMENTS 2014

MAIN ACHIEVEMENTS 2014

1. Relativistic Plasma Mode Detection in a Two-Dimensional Electron System with Exceeding Speed of Light Conductivity.
V.M. Muravev, P.A. Gusikhin, I.V. Andreev, I.V. Kukushkin

In a two-dimensional electron system with exceeding speed of light conductivity a novel weakly damped mode of plasma oscillations remaining weakly damped right up to room temperatures was detected. The conditions for its existence are high conductivity and the presence of close metal gate that indicates polariton nature. The mode has abnormal small width of the resonance absorption line. There are perspectives for fabrication of this mode based fast detectors and subterahertz radiation generators.

 

2. Coulomb Interaction in the Intersecting Electron Beams.
V.S. Khrapai, D.V. Shovkun, E.S. Tikhonov, M.U. Melnikov, G. Biasiol*, L. Sorba

Combination of carrier high quality and low density in modern semi-conductive structures enables to study Coulomb phenomena beyond Landau’s description (in fact, in pure limits).

In 2014 ISSP RAS researchers have made significant experimental progress in this direction using measurements of nonequilibrium current fluctuations and local bolometry.

A small aperture connecting pure two-dimensional electron reservoirs is sensible to inelastic electron-electron scattering in its vicinity due to the disturbance of detailed balance at current flow.

The analogue of drag effect between injected and incident electron beams exists; it leads to contact resistance reduction.
Shot noise studying at the same time allows to judge unambiguously about the key role of electron-electron scattering.

 

3. Current-Induced Magnetization Dynamics at the Edge of a Two-Dimensional Electron System with Strong Spin-Orbit Coupling
A. Kononov, S. V. Egorov, G. Biasiol, L. Sorba, and E. V. Deviatov

Electron transport is experimentally investigated through the interface between a permalloy ferromagnet and the edge of a two-dimensional electron system with strong Rashba-type spin-orbit coupling. Strongly nonlinear transport is observed around zero bias at milli-Kelvin temperatures. The observed nonlinearity is fully suppressed above some critical values of temperature, magnetic field, and current through the interface. This behavior is interpreted as the result of spin accumulation at the interface and its current-induced absorption as a magnetization torque. (Phys. Rev. B 89, 075312 (2014))

 

4. Resistive Switching and Diode Properties of Mesoscopic Niobium-Oxide-Based Structures.
N.A. Tulina, A.N. Rossolenko, I.Yu. Borisenko, I.M. Shmytko, A.M. Ionov, A.A. Ivanov

The fabrication technology is developed and the effects of resistive switchings in niobium-oxide-based structures are studied in ISSP.

I-V characteristics of heterostructures consisting of niobium oxide amorphous films have a weak resistive switching effect.

However, annealing shifts niobium oxide to the multiphase nanocrystalline state, and arising spatial inhomogeneity in oxygen vacancies leads to reversible switching from the low-resistive to the high-resistive state and the existence of bistable resistive states.

This effect is connected with Schottky barrier modulation on the metal-oxide interface.

5. The Novel Method for Production of Silicon-Carbide Ceramics Items
S.L. Shikunov, V.N. Kurlov

The novel method of multifunctional silicone-carbide ceramics production based on silicon melt interaction with carbon situated in a beforehand prepared blank with certain composition and porosity was developed in ISSP RAS.

Novel structural ceramics has higher operating temperatures, chemical stability, mechanical, thermo-shock and radiation resistance, wear resistance, reliability, service life and parameters stability.

It opens broad prospects for its use in chemical, oil-producing and oil-refining industry, and also its use as the components for gas-turbine engines of new generation.

Technologies and Equipment for Sapphire Large-Sized Crystal Growing for Wide-Aperture Optics of Aerospace Application, Transparent Armor, Protective Screens for Mobile Device Displays.
A.V. Borodin (ISSP RAS and EZAN RAS)

The technologies and equipment for growing of single-crystal sapphire in the form of plain windows with characteristic size up to 300 mm by Stepanov’s method for transmitting optics and shielding windows for guiding, tracing and recognizing devices and for transparent armor were developed. Technologies and equipment allow one to considerably improve efficiency and reduce prime cost of similar products.

7. 2D-Structures Based on Layered Gallium Chalcogenides
S. Schwarz, S. Dufferwiel, P. M. Walker, F. Withers, A. Trichet, M. Sich, F. Li, E. A. Chekhovich, D. N. Borisenko, N. N. Kolesnikov, K. S. Novoselov, M. S. Skolnick, J. M. Smith, D. N. Krizhanovskii, A. I. Tartakovskii
(ISSP RAS + University of Manchester, University of Sheffield)

The methods for GaS1-xSex (x = 0 – 1) layered single crystal growth by vertical zone melting under inert gas pressure were developed in ISSP. Exfoliation of such materials similarly to a grapheme allowed one to fabricate 2D-structures having the area up to 1500 µm2

Photoluminescence of obtained GaSe films ≫ 40 nm thick in microresonators with distributed Bragg reflectors from SiO2/TiO2 quarter-wavelength pairs was studied.

At wavelength of 603.7 nm 60-fold Purcell’s amplification of PL intensity in a resonator at the decrease in its damping time by an order of magnitude was observed experimentally.

 

MAIN ACHIEVEMENTS 2013

MAIN ACHIEVEMENTS 2013

On a New Type of Dirac Fermions in Crystalline Topological Insulators

Algebraic  topological methods are fruitfully applied to many problems from quantum field theory to condensed matter physics. Although the foundations of mathematical methods are common, the methods themselves can vary depending on the formulations of problems.

We briefly mention frequently used approaches. For example, the problem of the classification of structural defects and determination of their stability is reduced to the analysis of the equivalence classes of homotopic maps of a certain standard manifold associated with the bypass of a defect to the space of the order parameter. The classification is reduced to the list of homotopy groups associated with such maps.

The formulation of the problem for crystal insulators differs from those mentioned above and is mainly reduced to the following questions.

(i) What nontrivial features of the electron spectrum dictated by spatial symmetries and time reversal invariance are possible on the surface in these systems at the symmetric k points of the Brillouin zone(ZB)? They should not be present in the systematic of the bulk spectrum (should be beyond the projections of bulk bands, see below).

(ii) Are these singularities stable under continuous deformations of the Hamiltonian of the system under which the Hamiltonian is invariant under spatial symmetry elements and time reversal, and which do not close the gap in the projections of bulk bands? This leads to the so-called Z2 classification different from the mentioned  classification of torsions in the momentum space.

Fig.1. a) An example of two-dimensional lattice with nontrivial translations. b) Elements of lattice symmetry (the sliding planes are marked by dashed lines). c) Irreducible part of the Brillouin zone. d) A conical spectrum of the fourfold expressed fermions.

Until now, for crystalline 3D→2D, 2D→1D, and pure two-dimensional 2D systems, the features of the spectrum with two-fold degeneracy at the symmetrical points of the ZB (conical, ε ~ ±|k|; square, ε ~ ±|k|2; and cubic ε ~ ±|k|3) have been discussed. Conical features of the spectrum were detected experimentally in pure 2D systems (graphene), as well as in 3D→2D systems (BiSb binary compounds, and heteroboundaries between A4B6 and A2B6 semiconductors with band inversion), and  2D→1D crystal systems.

A question arises of whether conical features exist in crystalline systems with a higher degree of degeneracy. The study of the possibility of the appearance and experimental detection of such features (if they are possible) in crystalline 3D→2D, and pure 2D systems is an interesting topical problem.

Surface (edge) states with the conic dispersion law, and with more than two-fold degeneracy are absent in 2D→1D systems, because the groups of borders do not allow more than two-fold degeneracy because of the poverty of symmetry elements.

The ideal situation would be if particular materials, or compounds where a larger degree of degeneracy was possible could be presented. However, it is currently impossible. Nevertheless, it is possible to present a crystal structure of a compound with a conical massless spectrum with fourfold degeneracy.

This problem is solved in this work. Moreover, four-fold degeneracy of the conical spectrum turns out to be maximally allowable in 3D→2D systems.

(Laboratory of Semiconductor Surfaces Spectroscopy, Doctor Sci. of Physics and Mathematics, Prof. S. N. Molotkov)

 

Suppression of  Andreev  reflection  at energy levels  much lower  than  the super-conducting energy gap

Recently, there is a strong interest  in semiconductor hybrid systems which consist of a metal and a low-dimensional electron system. Such interest was originally caused by the problem of finding elementary excitations of a Majorana fermion type in a solid body.

Yet it turned out that the topological superconductivity mode that allowed such excitation caused special interest, both theoretically and experimentally.  The topological superconductivity mode emerges when the macroscopic order parameter penetrates the interface between a low-dimensional electron system with a strong spin-orbit coupling, and a superconductor.

So far, experimental results in this field have been controversial. They mainly refer to the case of one-dimensional systems, i.e. a quantum wire.

On the other hand, it is well-known that the edge of a two-dimensional electron system exhibits well-pronounced qualities of a one-dimensional transport both in quantizing and zero magnetic fields.  Therefore, a more general experimental task of investigating the transport through the interface between a two-dimensional electron system with a strong spin-orbital coupling, and a metal with a macroscopic order parameter can be set.

The charge transport through the interface between an edge of a two-dimensional electron system in a narrow quantum well InGaAs that exhibited a strong Rashba type spin-orbit coupling, and a metal with a macroscopic order parameter – a superconductor (Nb, or NbN) was investigated.

A partial suppression of Andreev reflection on the interface at super-cold temperatures (less than 300 mK), and small electrical bias was revealed. Analyzing the magneto-field and temperature dependencies provides a definitive interpretation of this suppression being the result of spin-orbit coupling in a two-dimensional system.

Also, a local interface conductivity peak at zero biases, located in a narrow area of magnetic fields that corresponded to the ones necessary for topological superconductivity realization (zero bias anomaly) was revealed. These results were partly (in the part of the first measures of the niobium contact) published in a work “Letters to Journal of Experimental and Theoretical Physics”, №98, Issue 7, 477-483 (2013).

(Laboratory of Quantum Transport, Doctor Sci. of Physics and Mathematics A. A. Shashkin)

 

Finite size effect in the shot noise in hopping conductivity

Under the condition of thermodynamic equilibrium, current fluctuations in a conductor are determined solely by its temperature and resistance (the Johnson-Nyquist thermal noise). In presence of an electric current non-equilibrium excess fluctuations occur, so-called shot noise.

Such noise results from the discreteness of the elementary charge, and is maximum for Poisson statistics of the charge flow. The conductance of a metallic and/or coherent conductors at low temperatures is determined by the elastic scattering processes. In such systems the shot noise is observed provided the size of the sample investigated is small compared with the energy relaxation length on which a local equilibrium is established.

Whether the shot noise exists in an insulator with a hopping conductivity at a finite temperature, and what's its  magnitude is not obvious.  In fact, the hopping conductivity itself is an inelastic process already on the scale of a single hop (~ 100 nm), that, presumably, should suppress the noise in macroscopic samples.

In this work the shot noise in a two-dimensional electronic system in GaAs in samples with a channel length of 5 um at temperatures in the range from 0.5 to 4.2K is investigated. Electronic density changes by means of a metallic front gate. At a low densities, an insulating state is achieved with the conductance temperature dependence corresponding to the Mott's variable range hopping regime. In such conditions the spectral density of the current noise is measured at frequencies above 10 MHz, which is about two orders of magnitude higher than all of the previous studies, allowing to reliably avoid the influence of the modulation/flicker noise.

At a temperature of 0.5K the conductivity falls roughly exponentially at decreasing the electron density, while the shot noise increases and reaches the Poisson value (Fano factor comparable to 1 for resistivity in the range of 10 MOhm per square). To our best knowledge, this is the first demonstration of a full shot noise in an insulator of a macroscopic size. It is also demonstrated for the first time that the shot noise significantly decreases when the temperature is increased (approximately a factor of 3 within the temperature range studied).

Fig.1 Fano factor grows along with sample depletion. The curves are vertically shifted for convenience. The scale on both axes should be multiplied by 5 and 50 for the middle and the lower curves correspondingly.

These results can be qualitatively explained by taking into account the features of the electric current flow in the VRH regime. It is well-known that the infinite current-carrying cluster is formed on the Miller-Abrahams random network with an exponentially wide spread of the hopping resistances. The correlation length  LC of such a cluster by far exceeds the average hop length, and determines the typical scale of the conductivity self-averaging.

In samples of the size smaller than LC the electric current flows along quasi-one-dimensional chains, with one highest hopping resistance dominating the resistance of each chain. As a result, the full current noise of a macroscopic sample is determined by such single hops, and reaches the Poisson value.  Based on experimental estimates of the localization length and Mott's temperature, the Poisson noise sets in at  LC ~ 1.5mkm, which is comparable to the sample size.

The fact that  LC decreases as the temperature and/or localization length increase explains qualitatively the observed decrease of the shot noise. At the same time, the shot noise decreases slower than the correlation length, which might be a result of poor self-averaging.

(Laboratory of Quantum Transport, Cand. Sci. of Physics and Mathematics V. S. Khrapai)

 

Nonlocal Supercurrent Observation in a Mesoscopic Structure with  Josephson Junction

The nanoelectronic superconductive devices that are being developed nowadays, are often under nonequilibriun conditions, since their size is comparable to such specific lengths as the length of nonequilibrium normal carrier conversion into cooper pairs lQ, spin diffusion length lS, et cetera.

The effect discussed is due to the  submicron Josephson planar junction (the SNS bridge located in the middle of the Figure) is fabricated near an normal carrier (quasi-particle) injector, so that the space d between the injector (N), and SNS junction was obviously smaller than  lQ, but significantly larger the superconducting coherence length xs.

When injecting the quasi-particles into the nearest superconducting aluminum bank of the SNS junction ‘bypassing’ the junction itself (the “nonlocal”  current pass) is marked by a dotted line in  the Figure), voltage over the junction was revealed when the electric current of the injection exceeded the critical value of Iinj,c.  The value of Iinj,c  was significantly higher than the normal critical current  Ic that was measured at the “local” current flow through the SNS junction (shown by a solid line in the Figure).

The upper part of the Figure shows an equivalent two-channel circuit that describes the occuring non-equilibrium processes, and corresponds to the theoretical model. The upper horizontal line represents the superconductive component. Its electrochemical potential only changes in the Josephson junction marked by the cross in the Figure.

On the contrary, electrochemical potential of the normal component (lower curve) changes along the whole structure. The presence of a non-equilibrium potential difference between the lines leads to conversion of the quasi-particles into Cooper pairs. This conversion is determined by an effective “cross conduction”  G=(RlQ2)-1, where R is the normal resistance per unit length of the aluminium strip.

Investigation within the framework of the suggested model shows that Ic/Iinj,c  ratio corresponds to the fraction of the injected quasi-particles that reach the SNS junction, and get compensated by counterflowing superconductive component, since the total current through the junction in the “non-local” experiment equals to zero. The discovered effect may be helpful for adjusting critical parameters in Josephson junctions by unbalanced currents in Josephson electronic diagrams.

(Laboratory of Superconductivity, Doctor Sci. of Physics and Mathematics V. V. Ryazanov)

 

Blowup dynamics of coherently driven polariton condensate

It was theoretically predicted basing on Gross-Pitaevskii equation that elastic parametric scattering can lead to energy accumulation of the polariton condensate under resonant and coherent optical pumping. The state of the condensate evolves in a peaking mode; slow intensity growth emerges at the point of the scattering threshold and gives way to burst-like explosive growth and transition to the upper stability branch in a finite amount of time. Therefore, a new, significantly nonlinear mechanism of quantum cavity  energy accumulation with a strong exiton-photon coupling was discovered. This mechanism reveals itself under photoexcitation with a comparatively large detuning of the pumping frequency from the polariton level.

During the process, the pumping amplitude weakly affected the finite amplitude of the cavity response, but it determined “the peaking period” that passed between the “switching on” of the pumping of the given amplitude and the rapid field enhancement. This period  varied in quite a wide range from several polariton lifetimes (under intensive pumping) to macroscopic amounts (near the scattering threshold).

Figure. “Time-suspended” effect of the transition between the stability branches of the bistable polariton condensate. The microcavity is excited along the cavity normal at 0.5 meV above the polariton level at resonance width of 0.04 MeV; a polariton lifetime makes 16 picoseconds. The pumping intensity exceeds the scattering threshold on 10%, but is 3 times lower that the transition threshold between the stability branches in a single-mode system (without scattering).

The upper part of the Figure illustrates the cavity field intensity vs time and planar projection of the wavevector (k = 0 corresponds to the excited mode); the lower left part shows the pumping intensity (dotted line) and the excited mode (solid line). The right part shows the resulting intensity of the scattered states vs time. Obviously, the slow energy accumulation of the scattered modes that occurred within 600 picoseconds under a strictly constant fixed outer pumping, ultimately lead to catastrophic field enhancement in the photoexcited mode itself.

The final response intensity is only 10% lower than the intensity that could have been obtained without time delay under a pumping intensity three times higher.

The here described effect mediates the mechanisms of non-equilibrium transitions, particularly the rapid spin conversion of polariton systems [1-3] in resonant-optical excitement. It is to be taken into consideration when developing optical switches and logical elements based on microcavities with a strong exiton-photon coupling.

1. S. S Gavrilov, A. V. Sekretenko et al., Applied Physics Letters 102, 011104, 2013.
2. S. S Gavrilov, A. V. Sekretenko et al.,  Phys. Rev. B 87, 201303, 2013.
3.  A. V. Sekretenko,  S. S Gavrilov et al., Phys. Rev. B 88, 205302, 2013
(Laboratory of Non-equilibrium Electronic Processes, Associated Member of RAS V.D. Kulakovskii)

 

Influence of Spin-Orbit Coupling on Electron Localization Effects

A crossover from weak localization at high temperatures to antilocalization at low temperatures was revealed in the temperature dependence of the two-dimensional hole-channel conductivity in silicon field transistors. We could describe the observed effect quantitatively, taking the change in the ratio of relaxation times of electron wave phases and spins when the temperature changes into account.

We analyzed how this effect is influenced by quantum corrections coming from the electron-electron coupling. The analysis indicated that there exists a parameter domain where the triplet contribution to the quantum correction to the conductivity of a two-dimensional electron system with a spin-orbital coupling is not suppressed by the electron-electron coupling.

Figure. Comparison of experimentally measured conductivity temperature dependences (symbols) with the calculated values: the dotted curves are the results calculated according to the weak- localization theory, and the solid curves are the calculation results with quantum corrections related to the electron-electron interaction in diffusion and ballistic modes taken into account (G. Zala, B.N. Narozhny, and I.L. Aleiner, Phys. Rev. B 64, 214204 (2001)), and without suppression of the triplet channel contribution by the diffusion mode electron-electron coupling. In all calculations, we used the times of the electron wave phase relaxation and spin-orbit relaxation, evaluated by measuring the nonmonotone anomalous magnetoresistance. (Nanolithography Sector, Doctor of Physical and Mathematical Science S. I. Dorozhkin)

Photonic liquid crystals

Epitomes of photonic liquid crystals were prepared. The theoretically predicted but never previously observed singularities linked to pendular oscillations in the diffraction spectra were discovered in the spectra of phase-delay(of the light polarization plane rotation).

It was shown that the photonic crystal optical characteristics linked to real and imaginary parts of permittivity could be described basing on universal Kramers-Kroning relations. The Δν  photonic band gap widths and their temperature dependence were determined. It was also shown that the temperature dependence of the photonic bandgap  Δν/ν0 relative width could be described using Landau theory of the first-order phase transition.

 


Figure1.TIF

Figure. Spectra of transmittance and phase-delay (of the light polarization plane rotation) of a cholesteric photonic crystal. The calculated and experimental spectra φ are marked by symbols and a solid curve.

(Laboratory of molecular structure spectroscopy, Candidate of Physical and Mathematical Sciences P. V. Dolganov)

 

Carbon nanotube arrays on metallic substrates

A device for producing carbon nanotube arrays (CNTAs) on metallic substrates  (RF Patent for the invention №2471706, 2013) was developed. Technological methods for producing CNT layers on stainless steel, electrotechnical steel and copper substrates were proposed.

The obtained structures are used as field emission cathodes (FEC) in scientific instruments for research in low-temperature physics. Such FECs  maintain their performance at temperatures ≤ 4 К. Nothing comparable to these FECs is currently known.

(Laboratory of Physical-Chemical Basis of Crystallization, Candidate of Technical Sciences N. N. Kolesnikov)

 

Nanostructured and nanoporous carbon-based materials obtained by globular SiO2 structure invertion.

Nanostructured carbon-based materials are attractive from both fundamental and practical points of view. They are widely used in many  technologies including electrode materials for supercapacitors, batteries and fuel elements, sorbents of various application and materials for catalysis. The most actively developed prospects are linked to  portable power supplies in microelectronics, energy storage systems, components for force pulsing devices and other instruments that require a high-speed energy source.

The key parameters of carbon-based materials used as electrodes in electrochemical energy sources are their specific surface area and the size and topology of their pores. The high specific surface area of carbon increases its capacity to store electric charge on its surface.

Micropores of at most 2 nm in diameter are the main component of its specific surface area. For quicker ion transport it is crucial to have mesopores (their diameter being from 2 to 50 nm) in the volume of the electrode material. The interconnected micro- and mesopore system combined with high electrode surface area raise the output characteristics of the devices.

Micro- and mesoporic carbon-based materials with specific surface area values close to their possible limit (2500 m2/g) and  pore volume up to 2 cm3/g got synthesized by the template method in ISSP RAS. An opal matrix represented by a three-dimensional close-packed system of monodispersed globular particles (globules) of silicone dioxide was used as a template.

The interconnected micro- and mesoporic system combined with the high surface area of an inverted opal improves both sorption properties and electrochemical output characteristics of the material. Figure 1 shows the synthesis scheme of silicone structures with an inverted opal network, and a fragment of the structure that demonstrates the interconnected pore system.

Fig. 1. Synthesis scheme and an inverted C-opal facet (111) cut.

It was shown that nanostructures have richer variety of properties including new functional properties when compared to the previously investigated materials. For example, spherical carbon particles containing graphite-like (onion-like) shells were discovered in the composite structures. The first investigation results allow an assumption that a diamond-like phase exists in an inverted opal SiC/C composite.

Carbon nanostructures with an inverted opal (C-IOP) network modified by tetraphenyl methilene diphosphine dioxide showed high sorption capacity towards Th (IV), U (VI) ions and lanthanides (III) in nitric acid solution, compared to the previously known sorbents. Table 1 shows the distribution ratio of Eu and  La/Lu separation factor for our sorbent and other carbon-based sorbents.

Table 1

Sorbent

C-IOP

Amberlite XADHP

Fullerene black

Carbon nanotubes

LogDEu

4.88

3.92

4.43

3.08

SFLa/Lu

109

8.7

52.5

85.1

(Laboratory of Crystallization from High-Temperature Solutions (LCHTS) G. A. Emelchenko)

Fundamental principles of laser  technologies, including material processing and modification, optical informatics, interconnection, navigation and medicine

Sapphire neurosurgical scalpel

Multichannel neurosurgical sapphire probe was invented in ISSP RAS.  The opened channels of the probe are used for suction, while the closed channels contain optical fibers along which coagulating laser radiation and diagnostic radiation is transmitted to the working tip of the instrument. Fluorophore diagnostics has significant advantages when brain tumor surgery is concerned.

The radiation is transported along the fibers from the laser radiation source to the distal end of the sapphire probe. On leaving the probe it gets internalized into the tissues which leads to their coagulation if the radiation power is high enough. The radiation wavelength is adjusted so that it does not get into the absorption bands of the fluorescent diagnostic agent. It is to prevent its burnout, and also for the penetration depth and zone size of the laser coagulation to be optimal for neurosurgery. The aspirator attached to the sapphire probe removes the brain tissue breakdown product from the diagnosed tumor zone.

The main advantage of the above-described device are as follows.

1. Several functions necessary for surgery are combined in one device.

2. The capabilities of the neurosurgical aspirator are enhanced by adding extra spectrometric fluorophore tissue diagnostics, applied interstitially as well. This allows to detect cancer cells appearing in the tissues objectively and timely, and determine how large the lesion site is and what tissue volume has to me removed.

3. It allows to eradicate brain tumors, makes surgical operations less traumatic, reduces blood loss and surgical intervention time by simultaneously demarking and removing the tumor and arresting the bleeding.

Sapphire neurosurgical probe and its application to brain tumor removal were developed in cooperation with members of the Neurosurgery Department of Moscow Regional Research and Clinical Institute n.a. M.F. Vladimirsky (MONIKI).  RF Patent was obtained for both the method and the device.

(Laboratory of Profiled Crystals, Doctor of Technical Sciences V.N. Kurlov)

 

MAIN ACHIEVEMENTS 2012

MAIN ACHIEVEMENTS 2012

Josephson magnetometry of weak low-temperature ferromagnets.
Weak low-temperature ferromagnets are actively used at present as Josephson barriers and magneto-active layers in cryo-switches and superconducting phase inverters, which have the prospect of use in superconducting electronics [1]. Magnetically soft weak ferromagnet (F) providing flow of superconducting current in Josephson superconductor-ferromagnetic-superconductor junctions (Josephson SFS junctions) is necessary for realization of Josephson magnetic switches [2]. Researches of Josephson SFS contacts based on weak ferromagnetic alloy Pd0.99Fe0.01with a Curie temperature of just 15 K have been initiated in Laboratory of Superconductivity at ISSP RAS [3]. Dependence of critical current Ic on applied magnetic field H for a Nb-PdFe-Nb SFS sandwich is shown in the figure. Dependence Ic(Ф) of Josephson junctions is periodic with respect to the magnetic flux Ф with a period corresponding to Ф00 is a magnetic flux quantum), that allows to build the magnetic field dependence of the flux Ф through the SFS junction (shown in the right inset). The magnetic flux in the plane of the Josephson F-layer is created as by the applied magnetic field H, and by the magnetization of the ferromagnetic layer M, and the contribution of the magnetization can be easily obtained by subtracting the magnetic flux through the junction. The obtained hysteresis loop of magnetization for thin (30 nm) layer of a weak ferromagnet with dimensions of 10 x 10 µm2 is shown in the left inset. It is easy to estimate that the saturation magnetic moment of the measured F-layer doesn't exceed 10-15 А-m2.

(Laboratory of Superconductivity, Dr. Phys.-Math. Sc., prof. V. V. Ryazanov)

 

The Mach-Zehnder interferometer with novel design of edge channels

The Mach-Zehnder interferometer with novel design of edge channels is created, which allows to observe an interference in the fractional quantum Hall effect regime. The device combines the advantages of the Mach-Zehnder and Fabry-Perot interferometers Its advantage is the fact that the only content of the interferential loop is quantum liquid with a fractional filling factor which greatly simplifies the analysis of the obtained experimental results.

Fig.1. Fig.2.

Operating principle of the interferometer in the fractional quantum Hall effect regime is shown in Fig.1. The upper part of the figure shows the part of a real sample visualized by means of a scanning electron microscope. The interferometer operates at a temperature of 30 mK in relatively strong magnetic fields. Figure 2 shows examples of interference patterns obtained for the integer filling factors when scanning the magnetic field and the gate voltage.


Fig.3

The corresponding interferograms for fractional filling factor are shown in fig.3.

As can be seen from this figure, for the filling factor 1/3 interference pattern appears particularly clearly. Also it was possible to observe interference with other fractional filling factors.


( Laboratory of Superconductivity, Dr. Phys.-Math. Sc., A.A.Shashkin)

Picosecond spin conversion in quasi two dimensional exciton-polariton systems

 

Quasi two dimensional exciton polaritons are composite bosons that emerge through strong exciton-photon coupling in flat semiconductor microresonators. Spin-related polariton-polariton interaction results in multistability and allows fast resonator response switching when the field values in the active layer reach their critical point. The physical reason for polariton multistability lays in spectrum renormalization with a shift of effective resonance frequency that significantly surpasses the resonance spectral width.

Normally, such conditions can only be achieved in a strong exciton-photon coupling mode. They  make polariton multistability effect qualitatively different from the previously studied optical multistability phenomena in lasers and other nonlinear media.

One of the key distinctions here is the strong sensitivity of the system to the initial resonance position which leads to new non-equilibrium transition scenarios in anisotropic or chiral polariton systems with split self-modes, for instance, due to Zeeman effect in the magnetic field.

We theoretically predicted and experimentally observed (see Fig.1) the effect of threshold spin-anisotropic spectrum renormalization of chiral exciton-polariton systems that related to the condensate mode occupation number. This effect lead to excited mode spin inversion at the scale of several polariton lifetimes (tens of picoseconds) under the conditions of resonance optical pumping with gradually changing intensity and constant polarization.

Due to this newly-discovered effect, a new type of compact and quick-operating optical switches and logic elements based on microresonators with a strong exciton-photon coupling can emerge.

 

Fig.1. The upper part shows a diagram of the system steady-state response depending on the optical pumping power, its circular polarization degree being rс=0.5 (circular polarization degree of the transmission signal is marked by color), and a chart of anticipated transitions between different stability branches (polarization is shown by ellipses).
The lower part of the Figure represents the measured and calculated time dependences of the intensity of right- and left-hand-polarized components of the resonator optical field, the pulsed pumping duration being 70 ps in magnetic field B=6 Т for W=2W0 (reversible polarization transition 1-2_-1), and W=4W0 (irreversible polarization transition with spin inversion); W0 is the threshold power of the instability development.

(Laboratory of Non-equilibrium Electronic Processes, RAS Associate Member V. D. Kulakovsky)

 



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