Nature of superconducting fluctuation in photo-excited systems

Abstract

The photo-excited state associated with superconducting fluctuation above the superconducting critical temperature $T_c$ is studied based on the time-dependent Ginzburg-Laundau approach. The excited state is created by an electric-field pulse and is probed by a weak secondary external field, which is treated by the linear response theory mimicking pump-probe spectroscopy experiments. The behavior is basically controlled by two relaxation rates: one is ${\gamma }_1$ proportional to the temperature measured from the critical point $T-T_c$ and the other is ${\gamma }_2$ proportional to the excitation intensity of the pump pulse. The excited state approaches the equilibrium state exponentially in a long time $t\gg {\gamma }_1^{-1}$, while in the intermediate time domain we find a power-law or logarithmic decay with different exponents for $t\ll {\gamma }_2^{-1}$ and ${\gamma }_2^{-1}\ll t\ll {\gamma }_1^{-1}$, even though the system is located away from the critical point. This is interpreted as the critical point in equilibrium being extended to a finite region in the excited situation. The parameter dependences on both the pump and probe currents are also systematically studied in all dimensions.

16 pages, 11 figures