Two-dimensional Janus 1T - CrXY ( X=S , Se, Te, Y=F</mml:…

Ferrovalley, spin, and piezoelectric polarizations are novel characteristics for electronic materials, and so far, there are few reports that these properties coexist in a single system. By first-principles calculations, we predict a series of highly stable intrinsic ferrovalley materials, i. e. , single layer CrXY (X=S, Se, Te, Y=F, Cl, Br, I) with large valley polarization up 76. 1 meV and appropriate Curie temperature higher than room temperature. For CrSF, the large bandgap of spin-up (spin-down) is as high as 1. 96 eV (3. 11 eV), which is beneficial for generating 100% spin polarized carriers by optical excitation or electrical gating. The quasianomalous valley Hall effect with valley contrast properties can be induced by compressive strain in CrSI and CrTeX (X=Cl, Br, I). Meanwhile, the large in-plane (-5. 78-3. 540. 16em{0ex}pm/V) and outside plane piezoelectric polarization (-5. 03-2. 530. 16em{0ex}pm/V) of CrXY are higher than most reported two-dimensional materials. Our work provides a pathway for a wide variety of applications in nanoelectronics, spintronics, valleytronics, piezoelectrics, and other demanding areas.