Strain-induced half-valley metals and topological phase transitions in 
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 monolayers 
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Huan, Hao; Yang, Xue; Zhao, Bin; Gao, Guanyi; Bao, Hairui; Yang, Zhongqin

doi:10.1103/physrevb.104.165427

Cited by 81 publications

(55 citation statements)

References 60 publications

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“…So, the rich electronic state and novel phase transitions can still be achieved in practice by strain. In fact, dual topological phase transition has been achieved in monolayer OsBr 2 by strain 16 . The sign-reversible valleydependent Berry phase effects and QAH/HVM states in septuple atomic monolayer VSi 2 N 4 has been achieved by strain 36 .…”

Section: Discussionmentioning

confidence: 99%

“…The Os atom has more stronger SOC effects than Ru atom, which may give rise to other novelty effects. Recently, monolayer OsBr 2 with 1H-MoS 2 type structure is predicted to stable 16 In this work, the electronic correlation effects on electronic structures of OsBr 2 monolayer are carefully investigated. Different from FeClF or FeCl 2 or RuBr 2 , increasing electron correlation induces threefold topological phase transition in monolayer OsBr 2 with intrinsic out-of-plane magnetic anisotropy, which means that there are three HVM states and two VQAHI regions.…”

Section: Introductionmentioning

confidence: 99%

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Correlation-driven threefold topological phase transition in monolayer $\mathrm{OsBr_2}$

Guo¹,

Mu²,

Liu³

2022

Preprint

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Spin-orbit coupling (SOC) combined with electronic correlation can induce topological phase transition, producing novel electronic states. Here, we investigate the impact of SOC combined with correlation effects on physical properties of monolayer OsBr2, based on first-principles calculations with generalized gradient approximation plus U (GGA+U ) approach. With intrinsic out-of-plane magnetic anisotropy, OsBr2 undergoes threefold topological phase transition with increasing U , and valley-polarized quantum anomalous Hall insulator (VQAHI) to half-valley-metal (HVM) to ferrovalley insulator (FVI) to HVM to VQAHI to HVM to FVI transitions can be induced. These topological phase transitions are connected with sign-reversible Berry curvature and band inversion between dxy/d x 2 −y 2 and d z 2 orbitals. Due to 6m2 symmetry, piezoelectric polarization of OsBr2 is confined along the in-plane armchair direction, and only one d11 is independent. For a given material, the correlation strength should be fixed, and OsBr2 may be a piezoelectric VQAHI (PVQAHI), piezoelectric HVM (PHVM) or piezoelectric FVI (PFVI). The valley polarization can be flipped by reversing the magnetization of Os atoms, and the ferrovalley (FV) and nontrivial topological properties will be suppressed by manipulating out-of-plane magnetization to in-plane one. In considered reasonable U range, the estimated Curie temperatures all are higher than room temperature. Our findings provide a comprehensive understanding on possible electronic states of OsBr2, and confirm that strong SOC combined with electronic correlation can induce multiple quantum phase transition.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Correlation-driven threefold topological phase transition in monolayer $\mathrm{OsBr_2}$

Guo¹,

Mu²,

Liu³

2022

Preprint

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“…Strain can modify the distance between atoms, and then can tune kinetic and interaction energies of electrons, which can induce topological transition [34][35][36] . The biaxial strain effects on QAH robustness of Fe 2 Br 2 are investigated, and a/a 0 (0.96-1.04) is used to simulate the biaxial strain with a/a 0 being the strained/unstrained lattice constants.…”

Section: Strain Effectsmentioning

confidence: 99%

“…These prove that the QAH state of monolayer Fe 2 Br 2 is robust against strain. Unlike Fe 2 Br 2 , strain can induce a series of phase transitions from ferrovalley (FV) insulator to half-valley metal (HVM) to QAHI in these 2D materials [34][35][36] , for example VSi 2 N 4 .…”

Section: Strain Effectsmentioning

confidence: 99%

Correlation-enhanced spin-orbit coupling and quantum anomalous Hall insulator with large band gap and stable ferromagnetism in monolayer $\mathrm{Fe_2Br_2}$

Guo¹,

Zhu²,

Liu³

2022

Preprint

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Nontrivial band topology combined with magnetic ordering can produce quantum anomalous Hall insulator (QAHI), which may lead to advances in device concepts. Here, through first-principles calculations, stable monolayer Fe2Br2 is predicted as a room-temperature large-gap high-Chernnumber QAHI by using generalized gradient approximation plus U (GGA+U ) approach. The large gap is due to correlation-enhanced spin-orbit coupling (SOC) effect of Fe atoms, which equates with artificially increasing the strength of SOC without electronic correlation. Out-of-plane magnetic anisotropy is very key to produce quantum anomalous Hall (QAH) state because in-plane magneitization will destroy nontrivial band topology. In the absence of SOC, Fe2Br2 is a half Dirac semimetal state protected by mirror symmetry, and the electronic correlation along with SOC effect creates QAH state with a sizable gap and two chiral edge modes. It is found that the QAH state is robust against biaxial strain (a/a0: 0.96 to 1.04) in monolayer Fe2Br2 with stable ferromagnetic (FM) ordering and out-of-plane magnetic anisotropy. Calculated results show that Curie temperature is sensitive to correlation strength and strain. The reduced correlation and compressive strain are in favour of high Curie temperature. These analysis and results can be readily extended to other monolayer Fe2XY (X/Y=Cl, Br and I), which possesses the same Fe-dominated low-energy states with a Fe2Br2 monolayer. These findings open new opportunities to design new high-temperature topological quantum devices.

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“…The QAH state in the VN 2 X 2 Y 2 nanosheets (X=B-Ga, Y=O-Te) can be induced by strain, and the valley polarization can also be switched from the bottom conduction band to the top valence band 9 . For monolayer MBr 2 (M=Ru and Os), compressive strain can induce phase transitions in the materials from FVS to HVM to VQAHI to HVM to FVS 10 . However, in these works, the intrinsic MAE as a function of strain has not been considered, and out-of-plane magnetic anisotropy is assumed to be fixed within considered strain range.…”

Section: Introductionmentioning

confidence: 99%

Strain effects on topological and valley properties of Janus monolayer $\mathrm{VSiGeN_4}$

Guo¹,

Mu²,

Wang³

et al. 2022

Preprint

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Strain is a very effective method to tune electronic states of two-dimension (2D) materials, which can induce unique phase transition. Recently, 2D MA2Z4 family materials are of interest because of their emerging topological, magnetic and superconducting properties. Here, we investigate the impact of strain effects (a/a0:0.96∼1.04) on physical properties of Janus monolayer VSiGeN4 as a derivative of VSi2N4 or VGe2N4, which possesses dynamic, mechanical and thermal stabilities. For out-of-plane magnetic anisotropy, with increasing strain, VSiGeN4 undergoes ferrovalley semiconductor (FVS), half-valley-metal (HVM), valley-polarized quantum anomalous Hall insulator (VQAHI), HVM and FVS. These imply twice topological phase transition, which are related with sign-reversible Berry curvature and band inversion between dxy+d x 2 −y 2 and d z 2 orbitals for K or -K valley. The band inversion also leads to transformation of valley splitting strength between valence and conduction bands. However, for in-plane magnetic anisotropy, no special quantum anomalous Hall (QAH) states and valley polarization exist within considered strain range. The actual magnetic anisotropy energy (MAE) shows that the easy magnetization axis of VSiGeN4 possesses a complex strain dependence, and several transitions in the magnetic anisotropy can be observed. The intrinsic phase diagram shows no special QAH and HVM states in monolayer VSiGeN4. Fortunately, these can be easily achieved by external magnetic field, which can adjust easy magnetization axis of VSiGeN4 from in-plane one to out-of-plane one. Because strain can effectively tune the correlation strength (U ) of electron, the MAE as a function of U is calculated, which shows similar outline with MAE vs a/a0. Our findings shed light on strain effects on electronic states of VSiGeN4, which may open new perspectives for multifunctional quantum devices in valleytronics and spintronics.

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Strain-induced half-valley metals and topological phase transitions in MBr2 monolayers (M=Ru,Os)

Cited by 81 publications

References 60 publications

Correlation-driven threefold topological phase transition in monolayer $\mathrm{OsBr_2}$

Correlation-driven threefold topological phase transition in monolayer $\mathrm{OsBr_2}$

Correlation-enhanced spin-orbit coupling and quantum anomalous Hall insulator with large band gap and stable ferromagnetism in monolayer $\mathrm{Fe_2Br_2}$

Strain effects on topological and valley properties of Janus monolayer $\mathrm{VSiGeN_4}$

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