Topo-photovoltaics Part 1

Light can be rectified to a direct current by inducing real-space shifts of quasiparticles in non-centrosymmetric materials. Shifts of quasi-particles arise in all dynamical, far-from-equilibrium processes of a photo-excited material, and these shifts are fundamentally related to the nontrivial twists of electronic wavefunctions in momentum space. Such twistings are characterized geometrically by the well-known intra-band Berry phase and the less-known inter-band Berry phase. Wave-function-enhanced photovoltaic currents can be utilized as an unprecedented phenomenological framework to faithfully diagnose topological materials, as we will exemplify with Z2 topological insulators (e.g., pressurized BiTeI), Dirac-Weyl fermions (e.g. multi-layer graphene) and Hopf insulators.