Circular Photon Drag Effect in Dirac electrons by Quantum Geometry

The bulk photovoltaic effect renders the need for the heterogeneous structure required in conventional p-n junctions, instead relying on intrinsic symmetry breaking within the homogeneous materials. For instance, in non-centrosymmetric materials, which breaks spatial inversion (P) symmetry, the emergent Berry curvature dipole and shift vector enable the generation of nonlinear injection and shift photocurrents. The intrinsic constraint of P-symmetry breaking can, however, be relaxed by introducing the photon-drag processes¹, where extrinsic momentum transfer from either photons or surface polaritons facilitates non-vertical optical transitions under oblique light incidence. In this work, we study the photon drag effect in Dirac electrons using the Riemannian geometry² on non-vertical optical transitions. Due to the particle-hole symmetry inherent in Dirac electrons, the shift photon-drag photocurrent is dominated by dissipationless Fermi surface contributions, connected to the dipole of quantum metric tensor. We find that this dipole is significantly enhanced by a small band gap in massive Dirac electrons and remains robust in the massless limit. We demonstrate the existence of a circular shift photon-drag current in the effective Hamiltonian at the L-point of bismuth, where the bands exhibit trivial topology, highlighting the ubiquity of the circular photon-drag effect even in centrosymmetric materials.