Superconducting gap anisotropy sensitive to nematic domains in FeSe

Takahiro Hashimoto,Shigeru Kasahara,Shuntaro Watanabe,Takahiro Shimojima,Shik Shin,Takasada Shibauchi,Chuangtian Chen,Yuji Matsuda,Haruyoshi Q Yamamoto,Yuya Suzuki,Yuichi Ota,Kozo Okazaki

doi:10.1038/s41467-017-02739-y

Takahiro Hashimoto, Shigeru Kasahara + Show 10 more

Open Access

https://doi.org/10.1038/s41467-017-02739-y

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Abstract

The structure of the superconducting gap in unconventional superconductors holds a key to understand the momentum-dependent pairing interactions. In superconducting FeSe, there have been controversial results reporting nodal and nodeless gap structures, raising a fundamental issue of pairing mechanisms of iron-based superconductivity. Here, by utilizing polarization-dependent laser-excited angle-resolved photoemission spectroscopy, we report a detailed momentum dependence of the gap in single- and multi-domain regions of orthorhombic FeSe crystals. We confirm that the superconducting gap has a twofold in-plane anisotropy, associated with the nematicity due to orbital ordering. In twinned regions, we clearly find finite gap minima near the vertices of the major axis of the elliptical zone-centered Fermi surface, indicating a nodeless state. In contrast, the single-domain gap drops steeply to zero in a narrow angle range, evidencing for nascent nodes. Such unusual node lifting in multi-domain regions can be explained by the nematicity-induced time-reversal symmetry breaking near the twin boundaries.

Highlights

The structure of the superconducting gap in unconventional superconductors holds a key to understand the momentum-dependent pairing interactions
We observe that the fourfold symmetry is significantly broken in the SC gap anisotropy, which is considered to be due to the orbital ordering, and find that while the SC gap node is not observed for multi-domain samples, it exists at the vertices of the major axis of the elliptical Fermi surface (FS) for single-domain samples
The number of impurities and defects was confirmed to be

Summary

Introduction

The structure of the superconducting gap in unconventional superconductors holds a key to understand the momentum-dependent pairing interactions. A study on the SC gap anisotropy of the zonecentered hole FS is presented based on the laser-excited ARPES measurements[26,27] of single-crystal FeSe. We observe that the fourfold symmetry is significantly broken in the SC gap anisotropy, which is considered to be due to the orbital ordering, and find that while the SC gap node is not observed for multi-domain samples, it exists at the vertices of the major axis of the elliptical FS for single-domain samples.

Results

Conclusion