nonlinear response in strongly-correlated electron systems*

Nonlinear responses in condensed matter are intensively studied today. While the nonlinear responses in noninteracting models have been explored widely, the effect of strong correlations on the nonlinear response is still poorly understood, even though it has been suggested that correlations can enhance the nonlinear response.[1-3]

In this work, we give an analytical derivation of nonlinear responses using the Green’s function methods at finite temperature, expand Parker's diagram methods[4] to the finite temperature, and compare the results to those by the semi-classical Boltzmann treatment and the reduced-density matrix method. We reveal that the relaxation time approximation, often used in the above two formalisms, leads to severe limitations when considering optical responses. Finally, we analyze the renormalization effect and lifetime differences in different orbitals and show they can yield large nonlinear responses.[5]

[1]H. Kishida, et al., Nature 405, 929-932(2000)
[2]S. Dzsaber, et al., arXiv: 1811.02819(2019)
[3]T. Morimoto and N. Nagaosa Scientific report 8,2973(2018)
[4]D. E. Parker, et al., PRB:99.045121(2019)
[5]YM and R. Peters, in preparation