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

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 MBr2 (M = Ru, 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 dxy/dx2-y2 and dz2 orbitals at K- and K+ valleys, analyzed based on a strained k center dot p model. Our work provides a pathway for carrying out low-dissipation electronics devices with complete spin and valley polarizations.

Automated summary

Research shows that MBr2 (M = Ru, Os) monolayers are ferrovalley materials with large valley polarization up to 530 meV, and compressive strain can induce phase transitions to complete valley-polarized metals, eventually forming Chern insulators, offering a pathway for low-dissipation electronics devices.