ARPES detection of superconducting gap sign in unconventional superconductors
Qiang Gao, Jin Mo Bok, Ping Ai, Jing Liu, Hongtao Yan, Xiangyu Luo, Yongqing Cai, Cong Li, Yang Wang, Chaohui Yin, Hao Chen, Genda Gu, Fengfeng Zhang, Feng Yang, Shenjin Zhang, Qinjun Peng, Zhihai Zhu, Guodong Liu, Zuyan Xu, Tao Xiang, Lin Zhao, Han-Yong Choi, Xingjiang Zhou
Abstract
Abstract The superconducting gap symmetry is crucial in understanding the underlying superconductivity mechanism. Angle-resolved photoemission spectroscopy (ARPES) has played a key role in determining the gap symmetry in unconventional superconductors. However, it has been considered so far that ARPES can only measure the magnitude of the superconducting gap but not its phase; the phase has to be detected by other phase-sensitive techniques. Here we propose a method to directly detect the superconducting gap sign by ARPES. This method is successfully validated in a cuprate superconductor Bi 2 Sr 2 CaCu 2 O 8+ δ with a well-known d -wave gap symmetry. When two bands have a strong interband interaction, the resulted electronic structures in the superconducting state are sensitive to the relative gap sign between the two bands. Our present work provides an approach to detect the gap sign and can be applied to various superconductors, particularly those with multiple orbitals like the iron-based superconductors.