In-plane anisotropy of the photon-helicity induced linear Hall effect in few-layer WTe2

Using Hall photovoltage measurements, we demonstrate that a linear transverse Hall voltage can be induced in few-layer WTe2 under circularly polarized light illumination. By applying a bias voltage along different crystal axes, we find that the photon-helicity induced Hall effect coincides with a particular crystal axis. Our results are consistent with the underlying Berry curvature exhibiting a dipolar distribution due to the breaking of crystal inversion symmetry. Using time-resolved optoelectronic autocorrelation spectroscopy, we find that the decay time of the detected Hall voltage exceeds the electron-phonon scattering time by orders of magnitude but is consistent with the comparatively long spin lifetime of carriers in the momentum-indirect electron and hole pockets in WTe2. Our observation suggests that a helicity induced nonequilibrium spin density on the Fermi surface after the initial charge carrier relaxation gives rise to a linear Hall effect.