Л†ВЈВ®Г Г¬, ВЇВ®ГЎГ«В« Г® ГўВҐВЎВҐ ВВВ®Гў Г¦ВЁГ® ГЎГў ГўГ¬ВЁ вЂљ ГЎГ®ГўВЁВ Е’

IV-curves of YBa₂Cu₃O_7-X monocrystals and Kosterlitz-Thouless` transition.
Vasutin M.A., Golovashkin A.I., Kuzmichev N.D., Levchenko I.S.

P.N. Lebedev Physics Institute of RAS, Moscow, Russia

Abstract

Nonlinear IV-curves of YBa₂Cu₃O_7-x single crystals in zero magnetic field have been investigated in the area of resistive transition to superconducting state. By Fourier-analysis modulation method the analytical form of the IV-curves was obtained at temperature T* which corresponds to maximum of the higher harmonics signal. The found dependence well describes the experimental results (IV-curves, amplitudes) at currents I < 30 mA (current density j < 310 A/cm²). In frame of the Kosterlitz-Thouless (KT) model it was shown that T* was equal the KT temperature T_KT. So we propose the new method of obtaining T_KT. It was shown that at T* the power approximation V ~ I³ was correct only at small currents (j вЂњ 140 A/ cm²). Deviation of IV-curves from the power dependence is connected with nonlogarithmic law of vortexes interaction.