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

Seng Huat Lee ,Venkatraman Gopalan ,Jin Hu ,Hemian Yi ,David Graf ,Hugh Churchill ,Aaron Wegner ,Nitin Samarth ,Yuanxi Wang ,Cui-Zu Chang ,Alessandra Lanzara ,Yi-Fan Zhao ,Arash Fereidouni ,Eun Sang Choi ,Rabindra Basnet ,Samuel Ciocys ,Ronald Redwing ,Katrina Verlinde ,Jingyang He ,Lujin Min ,Yanglin Zhu ,Zhiqiang Mao

doi: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.Received 21 June 2020Revised 25 April 2021Accepted 8 June 2021DOI:https://doi.org/10.1103/PhysRevX.11.031032Published 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 SocietyPhysics Subject Headings (PhySH)Research AreasAnomalous Hall effectMagnetotransportTopological insulatorsTopological materialsTopological phase transitionPhysical SystemsAntiferromagnetsSingle crystal materialsWeyl semimetalTechniquesAngle-resolved photoemission spectroscopyCrystal growthDC susceptibility measurementsEnergy spectroscopy for chemical analysisHall barMagnetization measurementsResistivity measurementsShubnikov-de Haas effectX-ray diffractionCondensed Matter, Materials & Applied Physics

Highlights

Weyl semimetals (WSMs) have become a forefront research topic in contemporary condensed matter physics [1,2,3]
The transition leads to an anomalous Hall effect (AHE) that we attribute to an intrinsic origin and a large negative c-axis longitudinal magnetoresistance that is consistent with the chiral anomaly
Prior studies of MnðBi1−xSbxÞ2Te4 [42,43] show that the carrier density is minimized near x ∼ 0.3, where the carrier type changes from electron to hole

Summary

INTRODUCTION

Weyl semimetals (WSMs) have become a forefront research topic in contemporary condensed matter physics [1,2,3] They provide model platforms for studying concepts in high-energy physics, such as the magnetic chiral anomaly effect. Theoretical studies show that the interlayer hybridization, combined with the protection of C3 rotational symmetry, induces band crossings in the FM phase, resulting in a single pair of strongly tilted, typeII Weyl cones with the Weyl nodes above the chemical potential [36,37]. The transition leads to an AHE that we attribute to an intrinsic origin and a large negative c-axis longitudinal magnetoresistance that is consistent with the chiral anomaly All these results provide strong support for the existence of the ideal Weyl state in the FM phase of this material

RESULTS AND DISCUSSION

Sample preparation and measurements

Analyses of anomalous Hall conductivity σAxyH and anomalous Hall angle ΘAxyH

Band structure calculations