Evidence of two-dimensional flat band at the surface of antiferromagnetic kagome metal FeSn

Minyong Han,Madhav Prasad Ghimire,Caolan John,Mun K Chan,Takehito Suzuki,Hisashi Inoue,Won Joon Cho,Joseph G Checkelsky,Efthimios Kaxiras,David Graf,Linda Ye,Shiang Fang

doi:10.1038/s41467-021-25705-1

Abstract

The kagome lattice has long been regarded as a theoretical framework that connects lattice geometry to unusual singularities in electronic structure. Transition metal kagome compounds have been recently identified as a promising material platform to investigate the long-sought electronic flat band. Here we report the signature of a two-dimensional flat band at the surface of antiferromagnetic kagome metal FeSn by means of planar tunneling spectroscopy. Employing a Schottky heterointerface of FeSn and an n-type semiconductor Nb-doped SrTiO3, we observe an anomalous enhancement in tunneling conductance within a finite energy range of FeSn. Our first-principles calculations show this is consistent with a spin-polarized flat band localized at the ferromagnetic kagome layer at the Schottky interface. The spectroscopic capability to characterize the electronic structure of a kagome compound at a thin film heterointerface will provide a unique opportunity to probe flat band induced phenomena in an energy-resolved fashion with simultaneous electrical tuning of its properties. Furthermore, the exotic surface state discussed herein is expected to manifest as peculiar spin-orbit torque signals in heterostructure-based spintronic devices.

Highlights

The kagome lattice has long been regarded as a theoretical framework that connects lattice geometry to unusual singularities in electronic structure
We investigate a flat band at the surface of antiferromagnetic kagome metal FeSn using planar tunneling spectroscopy
Cross-sectional transmission electron microscopy (TEM) and electron energy loss spectroscopy measurements corroborate that the films are highly crystalline down to the interface, which itself is comprised of the Fe kagome layer and Ti-rich termination layer of Nb-doped SrTiO3 (Nb):STO

Summary

Introduction

The kagome lattice has long been regarded as a theoretical framework that connects lattice geometry to unusual singularities in electronic structure. Transition metal kagome compounds have been recently identified as a promising material platform to investigate the longsought electronic flat band. There has been a growing interest in constructing a generalized lattice model that can universally produce flat bands through destructive phase interference of electronic hopping, even in the absence of compact atomic orbitals or high magnetic field[5,6,7,8,9,10,11,12]. Following decades of theoretical predictions, recent angle-resolved photoemission spectroscopy measurements on transition metal kagome compounds have shown that certain features in the twodimensional electronic structure of a single kagome layer manifest largely unperturbed in their three-dimensional electronic structures[13,21,22]. Kagome compounds with sufficiently large inter-layer hybridization[23,24,25,26], suggestive of the importance of strong electronic two-dimensionality in connecting to the original lattice model

Methods

Results

Conclusion