Janus TiXY Monolayers with Tunable Berry Curvature

Up to now, two-dimensional (2D) materials with both valley polarization and the Rashba effect are still rare. In this work, a new kind of Janus monolayers TiXY (X ≠ Y, X/Y = Cl, Br, I) is demonstrated to have physical properties of benefit for spintronics and valleytronics. In particular, Janus TiBrI shows Zeeman-type spin splitting of 70 meV, large Berry curvature of 106.22 bohr2, and, at the same time, a large Rashba parameter of 147.95 meV Å. On the basis of k · p perturbation theory, we proposed that the Berry curvature can be adjusted by changing the lattice parameter, which will greatly improve the transverse velocities of carriers and promote the efficiency of the valley Hall device. Biaxial strain from −2.5 to 2.5% was applied on Janus TiBrI to verify the theory mentioned above, and a general relationship between the Berry curvature and lattice constant was obtained.