Quantum anomalous Hall edge channels survive up to the Curie temperature

Kajetan M. Fijalkowski,Charles Gould,Steffen Schreyeck,Laurens W. Molenkamp,Karl Brunner,Nan Liu,Pankaj Mandal

doi:10.1038/s41467-021-25912-w

Kajetan M. Fijalkowski, Charles Gould + Show 5 more

Open Access

https://doi.org/10.1038/s41467-021-25912-w

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Journal: Nature Communications	Publication Date: Sep 22, 2021
Citations: 23	License type: open-access

Affiliation: University of Würzburg

Abstract

Achieving metrological precision of quantum anomalous Hall resistance quantization at zero magnetic field so far remains limited to temperatures of the order of 20 mK, while the Curie temperature in the involved material is as high as 20 K. The reason for this discrepancy remains one of the biggest open questions surrounding the effect, and is the focus of this article. Here we show, through a careful analysis of the non-local voltages on a multi-terminal Corbino geometry, that the chiral edge channels continue to exist without applied magnetic field up to the Curie temperature of bulk ferromagnetism of the magnetic topological insulator, and that thermally activated bulk conductance is responsible for this quantization breakdown. Our results offer important insights on the nature of the topological protection of these edge channels, provide an encouraging sign for potential applications, and establish the multi-terminal Corbino geometry as a powerful tool for the study of edge channel transport in topological materials.

Highlights

The metrological precision of Hall resistance quantization at zero magnetic field so far remains limited to temperature of the order of 20 mK15–17, while the Curie temperature (TC) in the involved materials is as high as 20 K2,3
As the Hall resistance takes on values clearly below h/e2 at temperatures above 1 K or so, well below TC, where the bulk remains robustly ferromagnetic, the nonquantized Hall resistance can in principle originate from the ordinary bulk states in the absence of any chiral edge channel
The structure is patterned from a 8.2 nm thick V0.1(Bi0.2Sb0.8)1.9Te3 layer grown by molecular beam epitaxy (MBE)[28], and optimized for exact anomalous Hall resistance quantization[15]

Summary

Introduction

Achieving metrological precision of quantum anomalous Hall resistance quantization at zero magnetic field so far remains limited to temperatures of the order of 20 mK, while the Curie temperature in the involved material is as high as 20 K. The main challenge for analyzing any results obtained from a traditional Hall bar, is the fact that the signals measured at the voltage leads can result from the current carried by both the edge channels and the bulk states in the material, making it impossible to definitively rule out contribution from the ordinary anomalous Hall effect.

Results

Conclusion