Nonlinear nonreciprocal photocurrents under phonon dressing

Abstract

Nonlinear optical (NLO) effects have attracted great interest recently. However, by far the computational studies on NLO use the independent particle approximation and ignore manybody effects. Here we develop a generic Green's function framework to calculate the NLO response functions, which can incorporate various many-body interactions. We focus on the electron-phonon coupling and reveal that phonon dressing can make significant impacts on nonlinear photocurrent, such as the bulk photovoltaic (BPV) and bulk spin photovoltaic (BSPV) currents. BPV/BSPV should be zero for centrosymmetric crystals, but when phonons are driven out-of-equilibrium, by for example, a temperature gradient ∇𝑇, the optical selections rules are altered and phonon-pumped BPV/BSPV currents can be non-zero in nominally centrosymmetric crystal. Moreover, we elucidate that such NLO responses under nonequilibrium phonon dressing can be nonreciprocal, as the direction of the current does not necessarily get reversed when the direction of the temperature gradient is reversed.

Shift Current with Gaussian Basis Sets and General Prescription for Maximally Symmetric Summations in the Irreducible Brillouin Zone

“…These quantities, or equivalently the corresponding third-rank tensors σ a ; bc (ω) as a function of a single frequency, admit expressions in terms of the quasiparticle properties that are amenable to numerical evaluation via quantum mechanical methods. Specifically, these microscopic expressions can be obtained by diagrammatic approaches for the ballistic current; − and by solving the density matrix perturbatively, employing Wilson loops or again by diagrammatic techniques for the injection and shift currents. However, only the latter one is truly intrinsic to the single-particle system, in the sense that it can be computed exclusively from the band structure and electronic eigenfunctions without further modeling.…”

Switchable Giant Bulk Photocurrents and Photo-spin-currents in Monolayer PT-Symmetric Antiferromagnet MnPSe3

“…In principle, the relaxation time τ might depend on k-points, band indices, and frequencies of light, because of impurity scattering, electron–phonons couplings, many-body interactions, etc. However, several previous studies have showed that it is still reasonable to consider an average and constant relaxation time approximation in the calculations of BPVEs. , Hence, in this study we adopt the constant relaxation time approximation and take the default value ℏ /τ = 1 meV; i.e., τ ≈ 0.6 ps. This setting is rather conservative since the MnPSe 3 is supposed to be a clean crystal due to its excellent chemical stabilities.…”

“…However, several previous studies have showed that it is still reasonable to consider an average and constant relaxation time approximation in the calculations of BPVEs. [39][40] Hence, in this study we adopt the constant relaxation time approximation and take the default value ℏ/𝜏 = 1 𝑚𝑒𝑉, i.e., τ≈0.6 ps by default. This setting is rather conservative since the MnPSe3 is supposed to be a clean crystal due to its excellent chemical stabilities.…”