Kazuhisa Hoshi — Page 2

arXiv2018

Indication of unconventional superconductivity in layered bismuth chalcogenide superconductor LaO0.6F0.4Bi(S,Se)2 revealed by Se isotope effect

We have investigated the Se isotope effect in layered bismuth chalcogenide (BiCh2-based) superconductor LaO0.6F0.4Bi(S,Se)2 with 76Se and 80Se. For all examined samples, the Se concentration, which is linked to the superconducting properties, is successfully controlled within x = 1.09-1.14 in LaO0.6F0.4BiS2-xSex. From the magnetization and electrical resistivity measurements, changes in Tc are not observed for the LaO0.6F0.4Bi(S,Se)2 samples with 76Se and 80Se isotopes. Our results suggest that pairing in the BiCh2-based superconductors is not mediated by phonons, and unconventional superconductivity states may emerge in the BiCh2 layers of LaO0.6F0.4Bi(S,Se)2.

cond-mat.supr-con↗

arXiv2017

Evolution of Anisotropic Displacement Parameters and Superconductivity with Chemical Pressure in BiS2-Based REO0.5F0.5BiS2 (RE = La, Ce, Pr, and Nd)

In order to understand the mechanisms behind the emergence of superconductivity by the chemical pressure effect in REO0.5F0.5BiS2 (RE = La, Ce, Pr, and Nd), where bulk superconductivity is induced by the substitutions with a smaller-radius RE, we performed synchrotron powder X-ray diffraction, and analyzed the crystal structure and anisotropic displacement parameters. With the decrease of the RE3+ ionic radius, the in-plane disorder of the S1 sites significantly decreased, very similar to the trend observed in the Se-substituted systems: LaO0.5F0.5BiS2-xSex and Eu0.5La0.5FBiS2-xSex. Therefore, the emergence of bulk superconductivity upon the suppression of the in-plane disorder at the chalcogen sites is a universal scenario for the BiCh2-based superconductors. In addition, we indicated that the amplitude of vibration along the c-axis of the in-plane chalcogen sites may be related to the Tc in the BiCh2-based superconductors.

cond-mat.supr-con↗