A.A. Zhukov,
M.R. Trunin, A.T. Sokolov, N.N. Kolesnikov.
Temperature dependence of surface
impedance of Tl2Ba2CaCuO8-d
and YBa2Cu3O6.95 single crystals measured
in the microwave band.
Abstract:
The real part Rs and the imaginary
part Xs of the surface impedance Zs=Rs+iXs
of
Tl2Ba2CaCuO8-d
and YBa2Cu3O6.95 single crystals
have been measured with high precision at frequency w/2p=9.4
GHz
in the temperature range 0< T<140 K. In the Tl2Ba2CaCuO8-d
crystal a linear temperature
dependence Rs (T) has been found for T
£
50 K, and the magnetic field penetration
depth l
(4.2 K)=Xs(4.2 K)/wm0
@
3760 Angstrom has been measured. Along with well known features of the
function Zs(T) in high-quality YBa2Cu3O6.95
single crystals, such as the linearity of l(T)
and Rs(T) for T<Tc/3 and a maximum
of Rs(T) at T ~ Tc/2, the linearity
range of l(T) extends to T @
50
K, and this curve has a plateau in the range
60<T<85 K. The curve of Rs (T)
in both the superconducting and normal states of YBa2Cu3O6.95
is well described by a two-fluid model with the electron-phonon mechanism
of quasiparticle relaxation. A formula describing the curve of
l2(0)/l2(T)
throughout the studied temperature range is also given.