Research
M.Sc. Project : I explored the nonlinear rotation of the polarization of light propagating in a 2D system. I used a density matrix framework to perturbatively calculate the induced polarization density, up to first and second order in the electric field strength. Using this I calculated the linear and non-linear optical conductivity. These conductivities go into Maxwell’s equations as material parameter inputs, for calculating the reflection and transmission coefficients of the optical beam interacting with the 2D material. I found that finite off-diagonal terms in the optical conductivity matrix induce Faraday and Kerr rotations in the reflected or transmitted optical beams .
Resonant bulk photogalvanic effect in centrosymmetric metals: My research works focus on nonlinear transport and optical phenomena in Topological materials. Currently, I am calculating third-order susceptibility in centrosymmetric systems. In centrosymmetric systems, the second-order photogalvanic responses vanish due to symmetry constraints which makes the third-order response the leading-order photogalvanic effect. We present a complete formalism for third-order susceptibility in optical limit for metallic or semi-metallic systems where a finite Fermi surface is present. There is no prior research in the literature on these kinds of responses. In addition to the third-order Jerk, shift, and injection current contributions that are expected in insulators as Fermi sea contributions, we also predict a novel sort of current contributions. In centrosymmetric semi-metallic systems where the second-order photogalvanic effects are identically zero and finite Fermi surface is present, our study provides a new perspective on the photogalvanic responses. The new current contributions can be seen in the following figure.
Fig: Schematic diagram of all the current contributions in third-order photogalvanic effect.
Intrinsic Third-Order Nonlinear Transport Responses: The recent discovery of new intrinsic transport coefficients in the second and third-order NL regimes has been a significant breakthrough, as these can be precisely calculated from ab initio methods and potentially relate to material topological properties. While the intrinsic anomalous Hall effect from Berry curvature was known for years, the recent addition of the BCP-induced NL Hall effect and intrinsic Fermi surface contributions for photogalvanic effects has expanded the list of intrinsic responses. In the third order, the study of intrinsic responses is ongoing, raising questions about their existence in inversion-symmetric systems, their dependence on band-geometric quantities, and their potential to reveal information about a material's magnetic state. This work aims to comprehensively investigate third-order intrinsic nonlinear transport coefficients, starting from a third harmonic generation calculation using quantum kinetic theory in the length gauge.
