论文标题
谷极化的量子异常大厅绝缘子$ \ mathrm {rubr_2} $
Valley-polarized quantum anomalous Hall insulator in monolayer $\mathrm{RuBr_2}$
论文作者
论文摘要
内在的Ferrovalley（FV）和非平凡带拓扑的共存引起了对其基本物理及其潜在应用的强烈兴趣，即Valley Polarled-Polarized量子异常霍尔绝缘子（VQAHI）。在这里，基于使用通用梯度近似以及$ u $（GGA+$ u $）方法的第一原理计算，通过电子相关或压力引起的vqahi可能发生在单层$ \ mathrm {rubr_2} $中。对于垂直的磁各向异性（PMA），将Ferrovalley（FV）到半谷基 - 金属（HVM）到量子异常大厅（QAH）到HVM到FV转变，可以通过增加电子相关性$ U $来驱动。但是，没有特殊的QAH状态和谷地磁各向异性的山谷极化。通过计算实际的磁各向异性能量（MAE），由于PMA，单位Chern数/手性边缘状态和自发山谷极化，VQAHI确实可以存在两个HVM状态之间。增加的$ u $可以诱导vqahi，可以通过$ d_ {xy} $/$ d_ {x^2-y^2} $和$ d_ {z^2} $ orbitals在$ d_ {xy} $/$ d_ {x^2-y^2} $之间来解释。即使真正的$ u $属于该系列的范围，也可以通过压力来实现vqahi。将$ u $$ = $ 2.25 ev作为具体情况，单层$ \ mathrm {rubr_2} $可以从普通的铁磁性（FM）半导体转变为约0.985压缩应变的VQAHI。值得注意的是，VQAHI的边缘状态是手性旋转 - 瓦利锁定，可以实现低径流电子设备的完全自旋和山谷极化。单层$ \ mathrm {rubr_2} $在单层中的能量带隙和山谷分裂都高于室温的热能（25 meV），这是设备应用的室温下的关键。
Coexistence of intrinsic ferrovalley (FV) and nontrivial band topology attracts intensive interest both for its fundamental physics and for its potential applications, namely valley-polarized quantum anomalous Hall insulator (VQAHI). Here, based on first-principles calculations by using generalized gradient approximation plus $U$ (GGA+$U$) approach, the VQAHI induced by electronic correlation or strain can occur in monolayer $\mathrm{RuBr_2}$. For perpendicular magnetic anisotropy (PMA), the ferrovalley (FV) to half-valley-metal (HVM) to quantum anomalous Hall (QAH) to HVM to FV transitions can be driven by increasing electron correlation $U$. However, there are no special QAH states and valley polarization for in-plane magnetic anisotropy. By calculating actual magnetic anisotropy energy (MAE), the VQAHI indeed can exist between two HVM states due to PMA, a unit Chern number/a chiral edge state and spontaneous valley polarization. The increasing $U$ can induce VQAHI, which can be explained by sign-reversible Berry curvature or band inversion between $d_{xy}$/$d_{x^2-y^2}$ and $d_{z^2}$ orbitals. Even though the real $U$ falls outside the range, the VQAHI can be achieved by strain. Taking $U$$=$2.25 eV as a concrete case, the monolayer $\mathrm{RuBr_2}$ 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 $\mathrm{RuBr_2}$ are higher than the thermal energy of room temperature (25 meV), which is key at room temperature for device applications.
