In-plane anisotropy of the <i>c</i>-axis magnetoresistance for BiCh₂-based superconductor

BiCh₂-based (Ch = S, Se) superconductor was discovered in 2012, the crystal structure is similar to that of high temperature superconductor, such as cuprate superconductor and iron-based superconductor. The pairing mechanisms of the superconductivity has not been completely understood. However, theoretical calculation, ARPES, and isotope effect suggest that unconventional superconductivity is essential for BiCh₂-based superconductor.
We have investigated the in-plane anisotropy measurement of the c-axis magnetoresistance for BiCh₂-based superconductor LaO_0.5F_0.5BiSSe single crystals. We observed the two-fold symmetry of the magnetoresistance in the ab-plane for LaO_0.5F_0.5BiSSe in superconducting states while the conducting plane possessed a tetragonal square plane with the four-fold symmetry. This results show that the BiCh₂-based superconductor may be nematic superconductor. Furthermore, more recently, we have investigated anisotropy measurement of the c-axis magnetoresistance for other BiCh₂-based superconductor NdO_0.7F_0.3BiS₂ single crystals. Two-fold symmetry was observed for NdO_0.7F_0.3BiS₂ above T_c, which is different behavior for LaO_0.5F_0.5BiSSe. We are going to report this latest result for the NdO_0.7F_0.3BiS₂ single crystals.