Magnetoresistance of Sr1−xKxBiO3: a second-family of bismuth-oxide-based superconductors

Abstract

The superconducting Sr1−xKxBiO3samples with x = 0.45 – 0.6 were synthesized by the high-pressure-high-temperature technique in a belt type apparatus (2 GPa, 700 °C, 1 h, Pt capsules) with stoichiometric mixtures of Sr2Bi2O5, Bi2O3and KO2as described earlier.1The X-ray diffraction results appear as a single perovskite-like phase. The superconductivity occurs at Tc∼ 12 K in the A. C. susceptibility measurement. The onset (zero resistivity) temperature of superconductivity in resistivity measurement of the investigated sample was\(T_{conset} = 12.5{\text{ }}K(T_{czero} = 10.2{\text{ }}K)\). The transition temperature region was a little bit broad and a shoulder was present about 11.3 K indicating probably the existence of crystallites of different K content. The particularly interesting point is that the resistance begins to reappear at T < 6 K at zero magnetic field. As the external magnetic field is applied, the reentrant resistance disappears and superconductivity is recovered until the applied magnetic field becomes higher than 0.65 Tesla. The superconductivity for T < 6 K is destroyed for the higher magnetic field. The Tconsetdecreases as the magnetic field increases like in the BCS type superconductors. The transition region becomes broader under the magnetic field, which indicate a kind of vortex transition as in the case of high Tccuprates.