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Evidence for a Magnetic-Field-Induced Ideal Type-II Weyl State in Antiferromagnetic Topological Insulator Mn(Bi1−xSbx)2Te4

Seng Huat Lee1,2, David Graf3,*, Lujin Min2,4, Yanglin Zhu1,2, Hemian Yi2, Samuel Ciocys5, Yuanxi Wang1,2, Eun Sang Choi3, Rabindra Basnet6 et al.

Arash Fereidouni6, Aaron Wegner6, Yi-Fan Zhao2, Katrina Verlinde4, Jingyang He2,4, Ronald Redwing1,4, V. Gopalan4, Hugh O. H. Churchill6, Alessandra Lanzara5, Nitin Samarth1,2, Cui-Zu Chang2, Jin Hu6,†, and Z. Q. Mao1,2,4,‡

  • 12D Crystal Consortium, Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
  • 2Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
  • 3National High Magnetic Field Lab, Tallahassee, Florida 32310, USA
  • 4Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
  • 5Department of Physics, University of California, Berkeley, Berkeley, California 94720, USA
  • 6Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA

  • *graf@magnet.fsu.edu
  • †jinhu@uark.edu
  • ‡zim1@psu.edu
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Phys. Rev. X 11, 031032 – Published 10 August, 2021

DOI: https://doi.org/10.1103/PhysRevX.11.031032

Abstract

The discovery of Weyl semimetals (WSMs) has fueled tremendous interest in condensed matter physics. The realization of WSMs requires the breaking of either inversion symmetry (IS) or time-reversal symmetry (TRS). WSMs can be categorized into type-I and type-II WSMs, which are characterized by untilted and strongly tilted Weyl cones, respectively. Type-I WSMs with breaking of either IS or TRS and type-II WSMs with solely broken IS have been realized experimentally, but a TRS-breaking type-II WSM still remains elusive. In this article, we report transport evidence for a TRS-breaking type-II WSM observed in the intrinsic antiferromagnetic topological insulator Mn(Bi1−xSbx)2Te4 under magnetic fields. This state is manifested by the electronic structure transition caused by the spin-flop transition. The transition results in an intrinsic anomalous Hall effect and negative c-axis longitudinal magnetoresistance attributable to the chiral anomaly in the ferromagnetic phases of lightly hole-doped samples. Our results establish a promising platform for exploring the underlying physics of the long-sought, ideal TRS-breaking type-II WSM.

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Popular Summary

Weyl semimetals are materials where the valence and conduction bands cross in single points, known as Weyl nodes. The discovery of Weyl semimetals has fueled tremendous interest in condensed-matter physics because they provide not only model platforms for studying concepts in high-energy physics but also a means of realizing technologically relevant exotic quantum states. Although Weyl semimetals have been demonstrated in several nonmagnetic and magnetic materials, one challenge in the current study of Weyl fermion physics is the lack of “ideal” Weyl semimetals. This article reports experimental evidence for the simplest ideal Weyl state, induced by magnetic fields in the antiferromagnetic topological insulator Mn(Bi1−xSbx)2Te4.

In an ideal Weyl semimetal, all the Weyl nodes are at the same energy level without interference from any other energy bands, and if the location of one pair of nodes in reciprocal space (the Fourier transform of real space) is known, the location of others can be found through symmetry operations. While ideal Weyl states have been long pursued, they have been realized only in bosonic systems such as photonic crystals.

We achieve such a Weyl state by tuning the Sb:Bi ratio. When the system is tuned to a state with a small hole concentration, we find the magnetic-field-induced transition from an antiferromagnetic state to a ferromagnetic one causes an electronic structure transition, which leads to transport properties characteristic of a Weyl state: an intrinsic anomalous Hall effect caused by effective magnetic fields in momentum space as well as negative magnetoresistance induced by parallel electric and magnetic fields.

These results establish an ideal model system for further understanding of Weyl fermion physics.

Article Text

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Phys. Rev. X 11, 031032– Published 10 August, 2021
  • Received 21 June 2020
  • Revised 25 April 2021
  • Accepted 8 June 2021
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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.

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