Strain-induced half-valley metals and topological phase transitions in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>M</mml:mi><mml:msub><mml:mi>Br</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> monolayers <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>(</mml:mo><mml:mi>M</mml:mi><mml:mo>=</mml:mo><mml:mi>Ru</mml:mi><mml:mo>,</mml:mo><mml:mspace width="4pt"/><mml:mi>Os</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:math>
H. Huan, Yang Xue, Bao Zhao, Guanyi Gao, Hairui Bao, Zhongqin Yang
Abstract
The target of valleytronics developments is to manipulate the valley degree of freedom and utilize it in microelectronics as charge and spin degrees of freedom. Based on first-principles calculations, we demonstrate that $M{\mathrm{Br}}_{2}$ $(M=\mathrm{Ru},\phantom{\rule{4pt}{0ex}}\mathrm{Os})$ monolayers are intrinsically ferrovalley materials with large valley polarization up to 530 meV. Compressive strain can induce phase transitions in the materials from ferrovalley insulators to complete valley-polarized metals, called half-valley metals, in analogy to the concept of half metals in spintronics. With the increase of the strain, the materials become Chern insulators, whose edge states are chiral-spin-valley locking. The phase transition is caused by sequent band inversions of the ${d}_{xy}/{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and ${d}_{{z}^{2}}$ orbitals at $K\ensuremath{-}$ and $K+$ valleys, analyzed based on a strained $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ model. Our work provides a pathway for carrying out low-dissipation electronics devices with complete spin and valley polarizations.