Reemergence of high-Tc superconductivity in the (Li1-xFex)OHFe1-ySe under high pressure

Jinhe Sun ,K Y Chen,N N Li,B S Wang,K Zhang,G M Zhang,Prashant Shahi ,Jiuyu Sun ,Fang Zhou ,Zhongxian Zhao ,Guangzong Xing ,Kui Jin ,Yoshiya Uwatoko ,Wenge Yang ,Songwei Ni ,Yanliang Huang ,Xianlin Dong ,Hui Zhou ,Jinguang Cheng

doi:10.1038/s41467-018-02843-7

Abstract

In order to elucidate pressure-induced second superconducting phase (SC-II) in AxFe2−ySe2 (A = K, Rb, Cs, and Tl) having an intrinsic phase separation, we perform a detailed high-pressure magnetotransport study on the isoelectronic, phase-pure (Li1−xFex)OHFe1−ySe single crystals. Here we show that its ambient-pressure superconducting phase (SC-I) with a critical temperature Tc ≈ 40 K is suppressed gradually to below 2 K and an SC-II phase emerges above Pc ≈ 5 GPa with Tc increasing progressively to above 50 K up to 12.5 GPa. Our high-precision resistivity data uncover a sharp transition of the normal state from Fermi liquid for SC-I to non-Fermi liquid for SC-II phase. In addition, the reemergence of high-Tc SC-II is found to accompany with a concurrent enhancement of electron carrier density. Without structural transition below 10 GPa, the observed SC-II with enhanced carrier density should be ascribed to an electronic origin presumably associated with pressure-induced Fermi surface reconstruction.

Highlights

In order to elucidate pressure-induced second superconducting phase (SC-II) in AxFe2−ySe2 (A = K, Rb, Cs, and Tl) having an intrinsic phase separation, we perform a detailed highpressure magnetotransport study on the isoelectronic, phase-pure (Li1−xFex)OHFe1−ySe single crystals
The superconducting mechanism for these SC-I phases has been subjected to extensive investigations, and the observed common Fermi surface (FS) topology consisting of only electron pocket in the Brillouin zone corners suggests that the electron doping plays an essential role for achieving high Tc9–11, in agreement with the gate-voltage regulation experiments on the FeSe flakes[12]
We find that the ambient-pressure SC-I phase is suppressed gradually with increasing pressure to Pc ≈ 5 GPa, above which a new SC-II phase with higher Tc over 50 K emerges gradually

Summary

Introduction

Without structural transition below 10 GPa, the observed SC-II with enhanced carrier density should be ascribed to an electronic origin presumably associated with pressure-induced Fermi surface reconstruction. When a single unit-cell FeSe film is fabricated on the SrTiO3 substrate, its Tc can be raised up to 65–100 K7,8 We refer these high-Tc superconductors derived directly from FeSe as the SC-I phase. High-pressure technique capable of both large pressure capacity and good hydrostaticity is required in order to obtain reliable superconducting- and normal-state properties. These complexities have hampered a proper understanding on the intriguing SC-II phase of these

Methods

Results

Conclusion