Abstract
Thin films promise new opportunities for the manipulation of surface states of topological semimetals with the potential to realize new states that cannot be obtained in bulk materials. Here, we report transport studies of gated Hall bar structures fabricated from approximately 50-nm-thick, (001)-oriented epitaxial films of cadmium arsenide, a prototype three-dimensional Dirac semimetal, in magnetic fields up to 45 T. The films exhibit a quantized Hall effect with pronounced odd-integer plateaus that is strikingly different from that of the more widely studied (112)-oriented films. We show that the unusual quantum Hall effect is a consequence of the inverted bulk band structure of cadmium arsenide that creates topological-insulator-like states at the bottom and top interfaces, each exhibiting a half-integer quantum Hall effect. A small potential offset between the two surfaces results in the crossing of the Landau levels and gives rise to the filling factor sequences observed in the experiments. Moreover, at large negative values of gate bias, the filling factor is abruptly preempted by an insulating state that is accompanied by the collapse of the well-developed quantum Hall effect. We suggest that this new phase cannot be explained within a single-particle picture and discuss the role of Coulomb interactions between spatially separated surface states.
- Received 10 July 2019
- Revised 25 November 2019
- Accepted 23 December 2019
DOI:https://doi.org/10.1103/PhysRevX.10.011050
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Three-dimensional Dirac semimetals—in which electronic band crossings lead to a low-energy realization of the Dirac equation, which ordinarily describes relativistic particles—are closely related to a variety of other topological phases. Moreover, interacting topological phases in a solid-state system are a highly sought-after goal in materials physics. This work focuses on cadmium arsenide, a prototypical 3D Dirac semimetal. Using extremely high magnetic fields and recent advances in epitaxial thin film growth, we discover a 3D topological insulator state in a thin film of a 3D Dirac semimetal.
The 3D insulating state is revealed by the integer quantum Hall effect in high magnetic field transport experiments on a cadmium arsenide thin film, in which the growth direction coincides with a specific crystal orientation—the sequence of Hall-effect plateaus provides a fingerprint of the zero-field band structure. We also discover a breakdown of the quantum Hall effect when the topological insulator surface states reach a characteristic carrier density, which we argue is mediated by Coulomb interactions or disorder.
This work represents a new state of the art in topological insulator thin films and topological semimetal thin films. Understanding the nature of the breakdown of the quantum Hall effect here may lead to a new class of interacting topological materials.