Fermi Surface Structure and Isotropic Stability of Fulde-Ferrell-Larkin-Ovchinnikov Phase in Layered Organic Superconductor β″-(BEDT-TTF)2SF5CH2CF2SO3

Shiori Sugiura,Shinya Uji,John A Schlueter,Yasuhiro Nakazawa,Syuma Yasuzuka,Taichi Terashima,Hiroki Akutsu

doi:10.3390/cryst11121525

Abstract

The Fermi surface structure of a layered organic superconductor β″-(BEDT-TTF)2SF5CH2CF2SO3 was determined by angular-dependent magnetoresistance oscillations measurements and band-structure calculations. This salt was found to have two small pockets with the same area: a deformed square hole pocket and an elliptic electron pocket. Characteristic corrugations in the field dependence of the interlayer resistance in the superconducting phase were observed at any in-plane field directions. The features were ascribed to the commensurability (CM) effect between the Josephson vortex lattice and the periodic nodal structure of the superconducting gap in the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase. The CM effect was observed in a similar field region for various in-plane field directions, in spite of the anisotropic nature of the Fermi surface. The results clearly showed that the FFLO phase stability is insensitive to the in-plane field directions.

Highlights

Published: 7 December 2021The discovery of superconductivity has led to breakthroughs in a wide range of fields from fundamental research and applications [1]
To investigate the 2D Fermi surface structure, we first measured the angular-dependent magnetoresistance oscillations (AMROs) in various rotation planes
We observed the CM effect in various in-plane field directions, which is recognized as strong evidence of the FFLO phase characterized by the q vector

Summary

Introduction

Published: 7 December 2021The discovery of superconductivity has led to breakthroughs in a wide range of fields from fundamental research and applications [1]. Since the discovery of high-temperature superconducting cuprates in 1980s, the search for new superconducting mechanisms has been one of the major trends in superconductivity basic research. Organic superconductors in the vicinity of metal-insulator transitions have brought about significant progress in basic research. Organic conductors based on BEDT-TTF molecules are characterized by a stacked structure with anion molecule (insulating) layers and BEDT-TTF molecule (conducting) layers. These conductors have attracted significant interest because of the presence of various ground states, a dimer-Mott insulating phase, a charge-ordered phase, a density wave phase, and a superconducting phase, where the degree of dimerization of the BEDT-TTF molecules, the Fermi surface instability, and the strong electron correlation play important roles. The possibility of unconventional superconductivity, mediated by antiferromagnetic spin and/or charge fluctuations, is a central concern

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