Observation of an electronic order along [110] direction in FeSe

Kunliang Bu,Yuan Zheng,Jun Zhao,Zongxiu Wu,Wenhao Zhang,Yi Yin,Ying Fei,Hongliang Wo,Qisi Wang,Fangzhou Ai

doi:10.1038/s41467-021-21318-w

Abstract

Multiple ordered states have been observed in unconventional superconductors. Here, we apply scanning tunneling microscopy to probe the intrinsic ordered states in FeSe, the structurally simplest iron-based superconductor. Besides the well-known nematic order along [100] direction, we observe a checkerboard charge order in the iron lattice, which we name a [110] electronic order in FeSe. The [110] electronic order is robust at 77 K, accompanied with the rather weak [100] nematic order. At 4.5 K, The [100] nematic order is enhanced, while the [110] electronic order forms domains with reduced correlation length. In addition, the collective [110] order is gaped around [−40, 40] meV at 4.5 K. The observation of this exotic electronic order may shed new light on the origin of the ordered states in FeSe.

Highlights

Multiple ordered states have been observed in unconventional superconductors
The intrinsic [100] nematic order is mainly detected at 4.5 K, consistent with previous Scanning tunneling microscopy (STM) experiments in which the order is determined from unidirectional signals around dumbbell defects57
The main discovery of this work is the observation of an intrinsic [110] electronic order at both 77 and 4.5 K

Summary

Introduction

We apply scanning tunneling microscopy to probe the intrinsic ordered states in FeSe, the structurally simplest iron-based superconductor. In iron-based superconductors, the [100] nematicity is usually accompanied with a collinear antiferromagnetic (AFM) order This long-range magnetic order is absent in bulk FeSe, raising a question whether other ordered states coexist and compete with the [100] order. We apply low-temperature STS to explore the intrinsic ordered states in bulk FeSe. A novel checkerboard charge order is observed in the iron lattice, which we name a [110] electronic order in FeSe. At liquid nitrogen temperature around 77 K, the robust [110] electronic order is accompanied with a weak [100] nematic order. The tradeoff effect implies a competition between the [100] and [110] electronic orders

Methods

Results

Conclusion