Highest Resolution Electrical Measurements

 

Dr. Xiaodong Zhou received his PhD in Physics from Physics Department of Tsinghua University, China in 2014. After a 3-year postdoctoral research at Columbia University, USA, he joined Fudan University, China in 2017 as an assistant professor. His primary research interest is in understanding the electronic and magnetic properties of quantum materials at microscopic scales using various scanning probe microscopes, such as scanning tunneling microscopy, magnetic force microscopy and scanning microwave impedance microscopy (sMIM).

 

In a just published Nature Communication paper co-lead by Dr. Xiaodong Zhou and Prof. Jian Shen from Fudan University, a metallic edge state was identified by sMIM in a layered topological antiferromagnet MnBi2Te4 at zero field, which challenges the axion insulator interpretation.

 

 

Visualizing an Unexpected Metallic Edge State in Even-layer MnBi2Te4 at Zero Field using LT ScanWaveTM

 

By Weiyan Lin et al. Nature Communications (2022)

 

Antiferromagnetic topological insulator (TI) MnBi2Te4 attracted considerable research interests in recent years for it represents the first intrinsic magnetic TIs-stoichiometric TIs with an innate magnetic orderso that topological phases can be studied in pristine crystals. In particular, MnBi2Te4 is a layered topological antiferromagnet consisting of Te-Bi-Te-Mn-Te-Bi-Te septuple layers (SLs) as the building block. Theory predicts an axion insulator - a topological phase showcasing quantized topological magnetoelectric effect-in atomically thin MnBi2Te4 flakes with even-layer thickness. Transport study reported a zero Hall plateau in 6-SL MnBi2Te4 supporting this axion insulator picture.

 

 

 

 

 

 

 

 

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Fig. 1. (a) The schematic of sMIM measurement. (b) Transport measurement shows zero Hall plateau in 6-SL MnBi2Te4. (c) sMIM imaging of a field driven topological phase transition in 6-SL MnBi2Te4, in particular its topological edge state at zero field.

 

sMIM has been demonstrated as a powerful tool to image topological edge states in various topological phases of matter. In this exemplary work, Weiyan Lin et al. combined transport and sMIM measurement to study 6-SL MnBi2Te4. In additional to the zero Hall plateau, the authors identified a metallic edge state at zero field, in conflict with the expectation of an axion insulator. A model calculation suggests a new topological phase-time-reversal-symmetry breaking quantum spin Hall (QSH) state - as the ground state for 6-SL MnBi2Te4 at zero field, which hosts a pair of gapped helical edge state explaining the sMIM findings. Moreover, the authors visualized a magnetic field driven topological phase transition from such a QSH state at zero field to a Chern insulator at high fields. This work highlights the importance of knowing the electronic states at microscopic levels, e.g., the topological edge states, in definitely determining a topological phase. sMIM holds a unique position in this endeavor.

 

To read the original publication of this paper, please visit Nature Communications.

 

Contact the author: Dr. Xiaodong Zhou.