Two-dimensional (2D) ferrovalley materials, displaying coexistence of spontaneous spin and valley polarizations, have recently attracted significant attention due to their potential for applications in the fields of spintronics and valleytronics. However, unfortunately, to date only a few 2D ferrovalley materials exist. Here, first-principles calculations predict a novel 2D Janus ferrovalley material, LaBrI. It is found that LaBrI is a stable ferromagnetic electride, whose magnetic moment originates mainly from the interstitial anionic electrons. The magnetic transition temperature of LaBrI monolayers is estimated to be far beyond room-temperature, and a sizeable magnetic anisotropy with easy in-plane magnetization is also present. Most importantly, LaBrI monolayers exhibit a large valley polarization due to the concurrent broken space-and time-reversal symmetry, with the calculated valley polarization reaching up to 59 meV. This value is comparable to that of the ferrovalley materials reported to date. Intriguingly, the inequivalent Berry curvature at the two valleys takes opposite values, giving rise to an anomalous valley Hall effect, where a valley current with an accompanying net charge Hall current may be induced.
Hydrogen-rich materials have fascinating physical and chemical properties such as various structures and superconductivity under high-pressure. In this study, structural, electronic, dynamical, and superconducting properties of GeH 4 (H 2 ) 2 are investigated based on the first-principles calculations. We first predict several phase transitions of GeH 4 (H 2 ) 2 under pressure. Below 28 GPa, two degenerated structures with I4̅ m2 and Pmn2 1 symmetries are preferred, which can be viewed as the distortion of the experimentally observed fcc structure. Then, the GeH 4 (H 2 ) 2 , via a triclinic phase that stabilizes in the pressure range of 28−48 GPa, transforms into a metallic orthorhombic phase in which appears the metallization induced by pressure. Another metallic phase with P2 1 /c symmetry enters the phase diagram at around 220 GPa, which is more stable than the case of a decomposed material, and its stability is also confirmed by including the zero point energy correction. In the high-pressure P2 1 /c phase, the superconductivity is found, and the superconducting transition temperature is predicted to be as high as 76−90 K at 250 GPa. This superconductivity mainly results from the local vibrations of more H 2 units, though the vibration of Ge in an H 2 -formed grid also contributes to the electron−phonon interaction. This study is helpful for understanding the superconducting mechanism on hydrogen-rich compounds.
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