Ultrafast four-wave mixing in strongly correlated electron systems

Abstract

We theoretically investigate the dynamics of photoexcited states in strongly correlated low-dimensional electron systems by analyzing the transient four-wave mixing (TFWM). We adopt the effective Hamiltonian of the Hubbard model for the photoexcited states in the strong correlation case, and TFWM intensity is obtained by numerically calculating the time development of the photoexcited state. We find that TFWM intensity sensitively reflects the relaxation due to the diffusion of the photogenerated charges and the relaxation due to the spin structure rearrangement to the diffused charge distribution. This enables us to clarify the interplay of charge and spin degrees of freedom. In the two-dimensional case, a well-separated two-step relaxation is observed; the slower spin relaxation follows the faster charge relaxation as a result of the coupling between the spin and charge degrees of freedom. This shows that the spin-charge separation approximately holds and the coupling between the spin and charge degrees of freedom is weak. In the one-dimensional case, only the charge relaxation is observed. Furthermore, there is no correlation between the relaxations before and after the second pulse. These are characteristic behaviors inherent in the spin-charge separation in strongly correlated electron systems.