Nonlinear terahertz electro-optical responses in centrosymmetric electronic systems

Understand

Motivated by the recent developments in terahertz spectroscopy using pump-probe setups to study correlated electronic materials, we review the field theoretical formalism to compute finite frequency nonlinear electro-optical responses in centrosymmetric systems starting from basic time dependent perturbation theory.

• We express the nonlinear current kernel as a sum of several causal response functions.
• These causal functions cannot be evaluated using perturbative field theory methods, since they are not contour ordered.
• Consequently, we associate each response function with a corresponding imaginary time ordered current correlation function, since the latter can be factorized using Wick's theorem.