Since the discovery of cuprate superconductors, layered compounds have been one of important target systems for developing new exotic superconductors and studying unconventional mechanisms. In this seminar, I will talk about material development of layered BiCh2-based (Ch: S, Se) superconductors, which were first discovered in 2012 [1,2]. In the BiCh2-based compounds, intrinsic local structural disorder (local distortion) has been observed by various experimental probes, and the suppression of local disorder is essential for the emergence of bulk superconductivity in the system . After obtaining bulk superconductors with less local disorder, we could see some interesting superconducting properties in BiCh2-based superconductors: absence of isotope effect , nematic superconductivity , and huge upper critical fields  in La(O,F)Bi(S,Se)2 will be briefly explained.
 Y. Mizuguchi et al., PRB 86, 220510 (2012)
 Y. Mizuguchi et al., JPSJ 81, 114725 (2012)
 (review article) Y. Mizuguchi, JPSJ 88, 041001 (2019)
 K. Hoshi, Y. Goto, Y. Mizuguchi, PRB 97, 094509 (2018)
 K. Hoshi et al., JPSJ 88, 033704 (2019)
 K. Hoshi et al., Sci. Rep. 12, 288 (2022)