Spectroscopic Evidence of Bilayer Splitting and Interlayer Pairing in an Iron Based Superconductor
Abstract
In high temperature cuprate superconductors, the interlayer coupling between the CuO planes plays an important role in dictating superconductivity, as indicated by the sensitive dependence of the critical temperature (T) on the number of CuO planes in one structural unit. In BiSrCaCuO superconductor with two CuO planes in one structural unit, the interaction between the two CuO planes gives rise to band splitting into two Fermi surface sheets (bilayer splitting) that have distinct superconducting gap. The iron based superconductors are composed of stacking of the FeAs/FeSe layers; whether the interlayer coupling can cause similar band splitting and its effect on superconductivity remain unclear. Here we report high resolution laser-based angle-resolved photoemission spectroscopy (ARPES) measurements on a newly discovered iron based superconductor, KCaFeAsF (T=33.5\,K) which consists of stacking FeAs blocks with two FeAs layers separated by insulating CaF blocks. Bilayer splitting effect is observed for the first time that gives rise to totally five hole-like Fermi surface sheets around the Brilliouin zone center. Band structure calculations reproduce the observed bilayer splitting by identifying interlayer interorbital interaction between the two FeAs layers within one FeAs block. All the hole-like pockets around the zone center exhibit Fermi surface-dependent and nodeless superconducting gap. The gap functions with short-range antiferromagetic fluctuations are proposed and the gap symmetry can be well understood when the interlayer pairing is considered. The particularly strong interlayer pairing is observed for one of the bands. Our observations provide key information on the interlayer coupling and interlayer pairing in understanding superconductivity in iron based superconductors.
Keywords
Cite
@article{arxiv.2001.04082,
title = {Spectroscopic Evidence of Bilayer Splitting and Interlayer Pairing in an Iron Based Superconductor},
author = {Dingsong Wu and Wenshan Hong and Chenxiao Dong and Xianxin Wu and Qiangtao Sui and Jianwei Huang and Qiang Gao and Cong Li and Chunyao Song and Hailan Luo and Chaohui Yin and Yu Xu and Xiangyu Luo and Yongqing Cai and Junjie Jia and Qingyan Wang and Yuan Huang and Guodong Liu and Shenjin Zhang and Fengfeng Zhang and Feng Yang and Zhimin Wang and Qinjun Peng and Zuyan Xu and Xianggang Qiu and Shiliang Li and Huiqian Luo and Jiangping Hu and Lin Zhao and X. J. Zhou},
journal= {arXiv preprint arXiv:2001.04082},
year = {2020}
}