Anisotropic upper critical field of the BiS2-based superconductor LaO0.5F0.5BiS2

作者：Mizuguchi Yoshikazu^*; Miyake Atsushi; Akiba Kazuto; Tokunaga Masashi; Kajitani Joe; Miura Osuke

来源：Physical Review B, 2014, 89(17): 174515.

DOI：10.1103/PhysRevB.89.174515

Superconducting properties under high magnetic fields for the BiS2-based layered superconductor LaO0.5F0.5BiS2 (polycrystalline sample prepared using the high-pressure synthesis method) are investigated. The anisotropy of the upper critical field is discussed by analyzing the temperature dependence of the temperature derivative of resistivity. The temperature dependence of the upper critical field shows an anomalous behavior with a characteristic magnetic field of 8 T. We reveal that the anomalous behavior is caused by the existence of three kinds of upper critical field mu H-0(C2)max, mu H-0(C2)mid, and mu H-0(C2)min in LaO0.5F0.5BiS2. The lowest upper critical field mu H-0(C2)min is regarded as mu H-0(c2), where the superconducting states of the grains with an orientation of H parallel to c are suppressed. The mu H-0(C2)max and mu H-0(C2)mid are regarded as mu H-0(c2), where the superconducting states of the grains with an orientation of H parallel to ab are suppressed. The difference between mu H-0(C2)max and mu H-0(C2)mid could be explained by the anisotropy of superconducting states within the Bi-S plane. The estimated anisotropy parameter of the upper critical fields is about 7.4 for the high-pressure-synthesized LaO0.5F0.5BiS2 polycrystalline sample. Since this value is clearly lower than the anisotropy parameter of over 30 observed in previously reported LaO0.5F0.5BiS2 single crystals grown under ambient pressure, we conclude that a larger anisotropy of superconductivity is not essential for the enhancement of T-c and lower anisotropy might be important for a higher T-c in LaO1-xFxBiS2.

• 出版日期2014-5-22