Unconventional superconductivity in the BiS$_2$-based layered superconductor NdO$_{0.71}$F$_{0.29}$BiS$_2

• Main Authors: Ota, Yuichi, Okazaki, Kozo, Yamamoto, Haruyoshi Q, Yamamoto, Takashi, Watanabe, Shuntaro, Chen, Chuangtian, Nagao, Masanori, Watauchi, Satoshi, Tanaka, Isao, Takano, Yoshihiko, Shin, Shik
• Format: Journal Article
• Language: English
• Published: 24.03.2017
• Subjects: Physics - Materials Science; Physics - Superconductivity
• DOI: 10.48550/arxiv.1703.08379

Phys. Rev. Lett. 118, 167002 (2017) We investigate the superconducting-gap anisotropy in one of the recently discovered BiS$_2$-based superconductors, NdO$_{0.71}$F$_{0.29}$BiS$_2$ ($T_c$ $\sim$ 5 K), using laser-based angle-resolved photoemission spectroscopy. Whereas the previously discovered high-$T_c$ superconductors such as copper oxides and iron-based superconductors, which are believed to have unconventional superconducting mechanisms, have $3d$ electrons in their conduction bands, the conduction band of BiS$_2$-based superconductors mainly consists of Bi 6$p$ electrons, and hence the conventional superconducting mechanism might be expected. Contrary to this expectation, we observe a strongly anisotropic superconducting gap. This result strongly suggests that the pairing mechanism for NdO$_{0.71}$F$_{0.29}$BiS$_2$ is unconventional one and we attribute the observed anisotropy to competitive or cooperative multiple paring interactions.