### Valley-dependent topological phase transition and quantum anomalous valley Hall effect in single-layer RuClBr

Hao Sun, Sheng-Shi Li, Wei-Xiao Ji,
Published: 9 May 2022

Abstract: Quantum anomalous valley Hall effect (QAVHE), which combines both the features of QAHE and AVHE, is both fundamentally intriguing and practically appealing, but is experimentally challenging to realize in two-dimensional (2D) intrinsic magnetic materials to date. Here, based on first-principles calculations with the density functional theory $+U$ approach, we predicted the electronic correlation-driven valley-dependent quantum phase transition from ferrovalley (FV) to half-valley-semiconductor (HVS) to QAVHE to HVS to FV phase in single-layer RuClBr. Remarkably, the QAVHE phase with an integer Chern number ($C=1$) and chiral spin-valley locking, which is induced by sign-reversible Berry curvature or band inversion between ${d}_{xy}/{d}_{{x}^{2}-{y}^{2}}$ and ${d}_{{z}^{2}}$ orbitals, can achieve complete spin and valley polarizations for low-dissipation electronics devices. We also find that the electron valley polarization can be switched by reversing magnetization direction, providing a route of magnetic control of the valley degree of freedom. An effective $k·p$ model is proposed to clarify valley-dependent quantum phenomena. Additionally, electronic correlation has an important effect on the variations of the Curie temperature of single-layer RuClBr. These findings shed light on the possible role of correlation effects on valley-dependent physics in 2D materials and open alternative perspectives for multifunctional spin-valley quantum devices in valleytronics.
Keywords: msub / msup / electronic correlation / valley dependent quantum / reversible / functional

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