Counterpropagating topological and quantum Hall edge channels

• Published in: Nature communications Vol. 13; no. 1; p. 2682
• Main Authors: Shamim, Saquib, Shekhar, Pragya, Beugeling, Wouter, Böttcher, Jan, Budewitz, Andreas, Mayer, Julian-Benedikt, Lunczer, Lukas, Hankiewicz, Ewelina M., Buhmann, Hartmut, Molenkamp, Laurens W.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 13.05.2022; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/119/2792/4128; 639/766/119/2794; Channels; Electromagnetism; Fabrication; Humanities and Social Sciences; Insulation; Inversion; Magnetic fields; Matter & antimatter; multidisciplinary; Puddles; Quantum Hall effect; Science; Science (multidisciplinary); Topological insulators
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-29815-2

The survival of the quantum spin Hall edge channels in presence of an external magnetic field has been a subject of experimental and theoretical research. The inversion of Landau levels that accommodates the quantum spin Hall effect is destroyed at a critical magnetic field, and a trivial insulating gap appears in the spectrum for stronger fields. In this work, we report the absence of this transport gap in disordered two dimensional topological insulators in perpendicular magnetic fields of up to 16 T. Instead, we observe that a topological edge channel (from band inversion) coexists with a counterpropagating quantum Hall edge channel for magnetic fields at which the transition to the insulating regime is expected. For larger fields, we observe only the quantum Hall edge channel with transverse resistance close to h / e 2 . By tuning the disorder using different fabrication processes, we find evidence that this unexpected ν  = 1 plateau originates from extended quantum Hall edge channels along a continuous network of charge puddles at the edges of the device. The quantum spin Hall effect disappears at high magnetic fields when the band inversion is lifted. The authors demonstrate that in contrast, in disordered samples, counter-propagating topological and quantum Hall edge channels prevent the detection of the trivial gap, explaining a previous observation.