Large valley-polarized state in single-layer NbX2 (X = S, Se): Theoretical prediction

Zang, Yanmei; Ma, Yandong; Peng, Rui; Wang, Hao; Huang, Baibiao; Dai, Ying

doi:10.1007/s12274-020-3121-1

Cited by 71 publications

(54 citation statements)

References 67 publications

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“…The time-reversal symmetry of two-dimensional (2D) magnetic semiconductors is naturally broken, which can give rise to spontaneous valley polarization together with the SOC interactions, namely FV material 12 . Many FV materials have been predicted by the density functional theory (DFT) calculations [13][14][15][16][17][18][19][20][21][22][23][24][25][26] . Recently, a new concept of HVM has been proposed 16 , being analogous to half metals in spintronics.…”

Section: Introductionmentioning

confidence: 99%

Valley-polarized quantum anomalous Hall insulator in monolayer $\mathrm{RuBr_2}$

Guo¹,

Mu²,

Liu³

2022

Preprint

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Coexistence of intrinsic ferrovalley (FV) and nontrivial band topology attracts intensive interest both for its fundamental physics and for its potential applications, namely valley-polarized quantum anomalous Hall insulator (VQAHI). Here, based on first-principles calculations by using generalized gradient approximation plus U (GGA+U ) approach, the VQAHI induced by electronic correlation or strain can occur in monolayer RuBr2. For perpendicular magnetic anisotropy (PMA), the ferrovalley (FV) to half-valley-metal (HVM) to quantum anomalous Hall (QAH) to HVM to FV transitions can be driven by increasing electron correlation U . However, there are no special QAH states and valley polarization for in-plane magnetic anisotropy. By calculating actual magnetic anisotropy energy (MAE), the VQAHI indeed can exist between two HVM states due to PMA, a unit Chern number/a chiral edge state and spontaneous valley polarization. The increasing U can induce VQAHI, which can be explained by sign-reversible Berry curvature or band inversion between dxy/d x 2 −y 2 and d z 2 orbitals. Even though the real U falls outside the range, the VQAHI can be achieved by strain. Taking U =2.25 eV as a concrete case, the monolayer RuBr2 can change from a common ferromagentic (FM) semiconductor to VQAHI under about 0.985 compressive strain. It is noted that the edge states of VQAHI are chiral-spin-valley locking, which can achieve complete spin and valley polarizations for low-dissipation electronics devices. Both energy band gap and valley splitting of VQAHI in monolayer RuBr2 are higher than the thermal energy of room temperature (25 meV), which is key at room temperature for device applications. It is found that electronic correlation or strain have important effects on Curie temperature of monolayer RuBr2. These results can be readily extended to other monolayer MXY (M = Ru, Os; X/Y=Cl, Br I). Our works emphasize the importance of electronic correlation and PMA to study FV materials, and provide a pathway to realize VQAHI.

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Section: Introductionmentioning

confidence: 99%

Valley-polarized quantum anomalous Hall insulator in monolayer $\mathrm{RuBr_2}$

Guo¹,

Mu²,

Liu³

2022

Preprint

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“…To achieve valley application, the external conditions, such as the optical pumping, magnetic field, magnetic substrates and magnetic doping [8][9][10][11] , have been used to trigger polarization. The FV materials may be the best choice for valleytronics due to spontaneous valley polarization 12 , and many FV materials have been predicted by the first-principle calculations [13][14][15][16][17][18][19][20] .…”

Section: Introductionmentioning

confidence: 99%

Sensitive electronic correlation effects on electronic properties in ferrovalley material Janus FeClF monolayer

Guo,

Zhu,

Yin

et al. 2021

Preprint

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The electronic correlation may have essential influence on electronic structures in some materials with special structure and localized orbital distribution. In this work, taking Janus monolayer FeClF as a concrete example, the correlation effects on its electronic structures are investigated by using generalized gradient approximation plus U (GGA+U ) approach. For perpendicular magnetic anisotropy (PMA), the increasing electron correlation effect can induce the ferrovalley (FV) to half-valley-metal (HVM) to quantum anomalous Hall (QAH) to HVM to FV transitions. For QAH state, there are a unit Chern number and a chiral edge state connecting the conduction and valence bands. The HVM state is at the boundary of the QAH phase, whose carriers are intrinsically 100% valley polarized. With the in-plane magnetic anisotropy, no special QAH states and prominent valley polarization are observed. However, for both out-of-plane and in-plane magnetic anisotropy, sign-reversible Berry curvature can be observed with increasing U . It is found that these phenomenons are related with the change of dxy/d x 2 −y 2 and d z 2 orbital distributions and different magnetocrystalline directions. It is also found that the magnetic anisotropy energy (MAE) and Curie temperature strongly depend on the U . With PMA, taking typical U =2.5 eV, the electron valley polarization can be observed with valley splitting of 109 meV, which can be switched by reversing the magnetization direction. The analysis and results can be readily extended to other nine members of monolayer FeXY (X/Y=F, Cl, Br and I) due to sharing the same Fe-dominated low-energy states and electronic correlations with FeClF monolayer. Our works emphasize the importance of electronic correlation to determine the electronic state of some materials, and the electronic correlation can induce exceptional phase transition.

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“…22,23 Up to now, only a few ferrovalley materials have been exposed in valley-polarized systems. To the best of our knowledge, candidate materials include 2H-VSe 2 , 21 2H-LaBr 2 , 24 2H-GdI 2 , 25 VAgP 2 Se 6 , 26 Nb 3 I 8 , 27 TiVI 6 , 28 VSi 2 N 4 , 29 Cr 2 COF, 30 and NbX 2 (X = S, Se), 31 as well as Janus 2H-VSSe, 32 and 2H-LaBrI. 33 In addition to feasibility for experimental fabrication, one key challenge in 2D intrinsic ferrovalley materials research for the integration of multiple electronic functionalities, is to achieve sizable valley polarization and high Curie temperature simultaneously.…”

Section: Introductionmentioning

confidence: 99%

Monolayer gadolinium halides, GdX₂ (X = F, Cl, Br): intrinsic ferrovalley materials with spontaneous spin and valley polarizations

Sheng

Yuan

Wang

2022

Phys. Chem. Chem. Phys.

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Large valley-polarized state in single-layer NbX2 (X = S, Se): Theoretical prediction

Cited by 71 publications

References 67 publications

Valley-polarized quantum anomalous Hall insulator in monolayer $\mathrm{RuBr_2}$

Valley-polarized quantum anomalous Hall insulator in monolayer $\mathrm{RuBr_2}$

Sensitive electronic correlation effects on electronic properties in ferrovalley material Janus FeClF monolayer

Monolayer gadolinium halides, GdX₂ (X = F, Cl, Br): intrinsic ferrovalley materials with spontaneous spin and valley polarizations

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Large valley-polarized state in single-layer NbX2 (X = S, Se): Theoretical prediction

Cited by 71 publications

References 67 publications

Valley-polarized quantum anomalous Hall insulator in monolayer $\mathrm{RuBr_2}$

Valley-polarized quantum anomalous Hall insulator in monolayer $\mathrm{RuBr_2}$

Sensitive electronic correlation effects on electronic properties in ferrovalley material Janus FeClF monolayer

Monolayer gadolinium halides, GdX2 (X = F, Cl, Br): intrinsic ferrovalley materials with spontaneous spin and valley polarizations

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Monolayer gadolinium halides, GdX₂ (X = F, Cl, Br): intrinsic ferrovalley materials with spontaneous spin and valley polarizations