Dynamics of Preformed Pairs and Transient Optical Conductivity in a Driven Attractive Hubbard Model

Ultrafast experiments on strongly coupled superconductors often report a superconductivity-like enhancement of low-frequency conductivity above . One proposed origin is the transient increase of the density of preformed pairs that survive without long-range phase coherence. To theoretically examine this picture, we study a light-driven 2D attractive Hubbard model using a t-matrix theory combined with the Floquet-Keldysh Green's function formalism. This framework allows us to investigate the dynamics of both electron and preformed pair degrees of freedom in the non-equilibrium steady state above . We calculate their non-equilibrium distributions, spectral weights, and the resulting optical conductivity. Our results aim to quantify the contribution of preformed pairs to the transient conductivity signals, providing new insights into the mechanisms of ultrafast optical responses in strongly coupled superconductors.