Low-energy effective theory and anomalous Hall effect in monolayer WTe₂

Monolayer WTe₂ in its 1T’ phase has been realized as a quantum spin Hall insulator with various intriguing properties such as superconductivity and non-linear Hall effect. We develop a symmetry-based effective low-energy theory for monolayer WTe₂ in its 1T’ phase. We find that to the leading order, the spin-orbit coupling in the k.p-theory near the gamma-point in the Brillouin zone is independent of the quasimomentum, and describes four fully spin-polarized bands, which are represented by two Kramers-partner pairs. Using the low-energy model, we study the spin susceptibility and time-dependent anomalous Hall effect induced by injected or equilibrium spin polarization in this system. We show that these measurements can help to determine the orientation of the conserved spin projection, the dimensionless tilt of band dispersion and the strength of the spin-orbit coupling of the system.