Tuning the interplay between nematicity and spin fluctuations in Na1\u2212xLixFeAs superconductors

S-H Baek,Bumsung Lee,B Büchner,Dilip Bhoi,Kee Hoon Kim,D V Efremov,Woohyun Nam

doi:10.1038/s41467-018-04471-7

Abstract

Strong interplay of spin and charge/orbital degrees of freedom is the fundamental characteristic of the iron-based superconductors (FeSCs), which leads to the emergence of a nematic state as a rule in the vicinity of the antiferromagnetic state. Despite intense debate for many years, however, whether nematicity is driven by spin or orbital fluctuations remains unsettled. Here, by use of transport, magnetization, and 75As nuclear magnetic resonance (NMR) measurements, we show a striking transformation of the relationship between nematicity and spin fluctuations (SFs) in Na1−xLixFeAs; For x ≤ 0.02, the nematic transition promotes SFs. In contrast, for x ≥ 0.03, the system undergoes a non-magnetic phase transition at a temperature T0 into a distinct nematic state that suppresses SFs. Such a drastic change of the spin fluctuation spectrum associated with nematicity by small doping is highly unusual, and provides insights into the origin and nature of nematicity in FeSCs.

Highlights

Strong interplay of spin and charge/orbital degrees of freedom is the fundamental characteristic of the iron-based superconductors (FeSCs), which leads to the emergence of a nematic state as a rule in the vicinity of the antiferromagnetic state
The magnetic scenario is believed to be realized in the 122family of FeSCs10–12, because a scaling relation was found between the spin fluctuations in nuclear magnetic resonance (NMR) and the shear modulus in the tetragonal phase of Ba(Fe1−xCox)2As210
NaFeAs is featured by the three successive transitions at low T; a nematic transition at Tnem~55 K is followed by a SDW at TSDW~45 K and by a filamentary SC transition at ~8 K

Summary

Introduction

Strong interplay of spin and charge/orbital degrees of freedom is the fundamental characteristic of the iron-based superconductors (FeSCs), which leads to the emergence of a nematic state as a rule in the vicinity of the antiferromagnetic state. In FeSCs other than FeSe, the SDW transition temperature TSDW is quite close to the nematic one Tnem, imposing limitations on investigating the interplay of nematicity and SFs in detail.

Results

Conclusion