Phase shift and magnetic anisotropy induced field splitting of impurity states in (Li1-xFex)OHFeSe superconductor

TL;DR

This study uses high-resolution STM/STS to analyze impurity-induced Yu-Shiba-Rusinov states in (Li1-xFex)OHFeSe, revealing magnetic anisotropy effects on in-gap state splitting under magnetic fields.

Contribution

It demonstrates the first high-resolution observation of YSR states with phase-energy correlation and reveals magnetic anisotropy's role in impurity state splitting.

Findings

Detection of two pairs of in-gap states with phase-energy correlation

Field-dependent splitting of impurity states influenced by magnetic anisotropy

Numerical models confirm high-spin impurity coupling causes anisotropic splitting

Abstract

Revealing the energy and spatial characteristics of impurity induced states in superconductors is essential for understanding their mechanism and fabricating new quantum state by manipulating impurities. Here by using high-resolution scanning tunneling microscopy/spectroscopy, we investigated the spatial distribution and magnetic field response of the impurity states in (Li1-xFex)OHFeSe. We detected two pairs of strong in-gap states on the "dumbbell" shaped defects. They display clear damped oscillations with different phase shifts and a direct phase-energy correlation. These features have long been predicted for classical Yu-Shiba-Rusinov (YSR) state, which are demonstrated here with unprecedented resolution for the first time. Moreover, upon applying magnetic field, all the in-gap state peaks remarkably split into two rather than shift, and the splitting strength is field orientation dependent. Via detailed numerical model calculations, we found such anisotropic splitting behavior can be naturally induced by a high-spin impurity coupled to anisotropic environment, highlighting how magnetic anisotropy affects the behavior of YSR states.