The Stratified Superconductivity in Ba0.6K0.4BiO3Single Crystal: Direct Measurement of Energy Gap between Homo-, and Inhomogeneous States

L N Zherikhina,S I Popkov,A M Tskhovrebov,K A Shaikhutdinov,L A Klinkova,D A Balaev,D A Velikanov

doi:10.1155/2014/317974

Abstract

The existence of space inhomogeneous superconductor insulator state (SISIS) found out earlier in polycrystalline samples of high-TCsystemBa0.6K0.4BiO3(TC≈30 K) is confirmed onBa0.6K0.4BiO3single crystal. AtT*(T*<TC,T*≈17 K) the transition from the homogeneous superconducting state into the SISIS occurs. SISIS is characterized by the appearance of two gaps on the Fermi surface, semi- and superconducting, which are modulated in space in antiphase, the electric transport between superconducting regions being carried out due to Josephson tunneling. Thus the whole sample becomes a multiple Josephson system. NonlinearI-Vcurves are observed onBa0.6K0.4BiO3single crystal at temperatures belowT*. Dependence ofI-Vcurves on temperature and magnetic field, typical to a Josephson system, was found out. Besides, a step-like peculiarity at the values of voltage of the order of one and two superconducting gaps shows up. These peculiarities are suppressed by magnetic field much earlier than critical current. The new data firstly correlate with the model of SISIS and secondly permit for the first time to determining directly the energy gap between homogeneous and stratified superconductor states.

Highlights

High-temperature superconductor (HTSC) Ba0.6K0.4BiO3 has a cubic lattice and has no copper atoms or any other magnetic ions. These features distinguish it from other HTSC compounds and do not allow one to justify its HTSC properties on the bases of layered structure or internal magnetic ions
The list displayed below illustrates this thematic latitude: (i) problems of synthesis, composition, and structure of high-TC Ba0.6K0.4BiO3 [6,7,8,9,10,11]; (ii) transport, phonon, and electron-phonon effects [12,13,14]; (iii) heat capacity, thermal expansion, and so forth [15,16,17,18,19,20]; (iv) investigation of magnetic response, accompanying superconducting transition, anisotropy of magnetic properties, and irreversibility effects in remagnetization [21,22,23,24]; International Journal of Superconductivity
At the same time we have found a number of unusual anomalies in behaviour of Ba0.6K0.4BiO3 investigated initially in polycrystalline form

Summary

Introduction

High-temperature superconductor (HTSC) Ba0.6K0.4BiO3 has a cubic lattice and has no copper atoms or any other magnetic ions (has been found out in 1988 [1, 2]). The anomalous temperature dependence R = R(T) and IC = IC(T), the hysteresis of the I-V curves (Figures 1 and 3 inset), and presence of superconducting phase in resistive state (Figure 2) can be explained in terms

Results

Conclusion