Visualizing atomic structure and magnetism of 2D magnetic insulators via tunneling through graphene

Zhizhan Qiu,Matthew Holwill,Huimin Yang,Mikhail Kashchenko,Jiong Lu,Pin Lyu,Jing Li,Hanyan Fang,Thomas Olsen,Kostya S Novoselov

doi:10.1038/s41467-020-20376-w

Abstract

The discovery of two-dimensional (2D) magnetism combined with van der Waals (vdW) heterostructure engineering offers unprecedented opportunities for creating artificial magnetic structures with non-trivial magnetic textures. Further progress hinges on deep understanding of electronic and magnetic properties of 2D magnets at the atomic scale. Although local electronic properties can be probed by scanning tunneling microscopy/spectroscopy (STM/STS), its application to investigate 2D magnetic insulators remains elusive due to absence of a conducting path and their extreme air sensitivity. Here we demonstrate that few-layer CrI3 (FL-CrI3) covered by graphene can be characterized electronically and magnetically via STM by exploiting the transparency of graphene to tunneling electrons. STS reveals electronic structures of FL-CrI3 including flat bands responsible for its magnetic state. AFM-to-FM transition of FL-CrI3 can be visualized through the magnetic field dependent moiré contrast in the dI/dV maps due to a change of the electronic hybridization between graphene and spin-polarised CrI3 bands with different interlayer magnetic coupling. Our findings provide a general route to probe atomic-scale electronic and magnetic properties of 2D magnetic insulators for future spintronics and quantum technology applications.

Highlights

The discovery of two-dimensional (2D) magnetism combined with van der Waals heterostructure engineering offers unprecedented opportunities for creating artificial magnetic structures with non-trivial magnetic textures
It is very likely that the underlying few-layer CrI3 (FL-CrI3) dominates the Scanning tunneling microscopy (STM) contrast at this particular sample bias Vs = 1V, which will be explained in detail later
We explored local electronic structures of G/FL-CrI3/Gr using scanning tunneling spectroscopy (STS). dI/dV spectrum taken over G/ FL-CrI3/Gr (Fig. 2a) reveals two prominent double-peak features above Fermi level (EF), which are labeled as C1 (0.3 V < Vs < 1.1 V) and C2 (1.1 V < Vs < 1.8 V), respectively

Summary

Introduction

The discovery of two-dimensional (2D) magnetism combined with van der Waals (vdW) heterostructure engineering offers unprecedented opportunities for creating artificial magnetic structures with non-trivial magnetic textures. We demonstrate that the application of vdW technology to the STM will dramatically expand the capabilities of the latter, allowing it to study insulating materials and gaining information about the magnetic ordering in 2D ferromagnets[6,7,8,9]. To this end, we assemble vdW heterostructures based on investigated 2D materials covered with monolayer graphene. The projection of the electronic states of other materials on graphene depends strongly on the atomic arrangements; additional information (like stacking between buried layers, or even information about magnetic structure) can be extracted from the close examination of the moiré structure between graphene and materials under study

Methods

Results

Conclusion