Unconventional Superconductivity in the BiS2-Based Layered Superconductor NdO(0.71)F(0.2)9BiS(2)

摘要

We investigate the superconducting-gap anisotropy in one of the recently discovered BiS2-based superconductors, NdO0.71F0.29BiS2 (T-c similar to 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 BiS2-based superconductors mainly consists of Bi 6p 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 NdO0.71F0.29BiS2 is an unconventional one and we attribute the observed anisotropy to competitive or cooperative multiple paring interactions.