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.