Valley polarization transition driven by biaxial strain in Janus $\mathrm{GdClF}$ monolayer

Abstract

The valley degrees of freedom of carriers in crystals is useful to process information and perform logic operations, and it is a key factor for valley application to realize the valley polarization. Here, we propose a model that the valley polarization transition at different valley points (-K and K points) is produced by biaxial strain. By the first-principle calculations, we illustrate our idea with a concrete example of Janus $\mathrm{GdClF}$ monolayer. The predicted $\mathrm{GdClF}$ monolayer is dynamically, mechanically and thermally stable, and is a ferromagnetic (FM) semiconductor with perpendicular magnetic anisotropy (PMA), valence band maximum (VBM) at valley points and high Curie temperature ($T_C$). Due to its intrinsic ferromagnetism and spin orbital coupling (SOC), a spontaneous valley polarization will be induced, but the valley splitting is only -3.1 meV, which provides an opportunity to achieve valley polarization transition at different valley points by strain. In considered strain range ($a/a_0$: 0.94$\sim$1.06), the strained GdClF monolayer has always energy bandgap, strong FM coupling and PMA. The compressive strain is in favour of -K valley polarization, while the tensile strain makes for K valley polarization. The corresponding valley splitting at 0.96 and 1.04 strain are -44.5 meV and 29.4 meV, which are higher than the thermal energy of room temperature (25 meV). Due to special Janus structure, both in-plane and out-of-plane piezoelectric polarizations can be observed. It is found that the direction of in-plane piezoelectric polarizations can be overturned by strain, and the $d_{11}$ at 0.96 and 1.04 strain are -1.37 pm/V and 2.05 pm/V. Our works pave the way to design the ferrovalley material as multifunctional valleytronics and piezoelectric devices by strain.

9 pages, 10 figures. arXiv admin note: text overlap with arXiv:2109.13534

References in corpus (7)

• Valley polarization in MoS2 monolayers by optical pumping
• Valley Dependent Optoelectronics from Inversion Symmetry Breaking
• Breaking of valley degeneracy by magnetic field in monolayer MoSe2
• Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS2
• Valley-related multiple Hall effect in single-layer VSi2P4
• Sign-reversible valley-dependent Berry phase effects in 2D valley-half-semiconductors
• Intrinsic piezoelectricity in monolayer $\mathrm{XS}{\mathrm{i}}_2{\mathrm{N}}_4$ (X=Ti, Zr, Hf, Cr, Mo and W)

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• Gadolinium halide monolayers: a fertile family of two-dimensional 4f magnets
• When Energy and Information Revolutions Meet 2D Janus
• Possible structural and bond reconstruction in 2D ferromagnetic semiconductor VSe2 under uniaxial stress