Nature of the superconducting fluctuations in photoexcited systems

Abstract

The photoexcited state associated with superconducting fluctuations above the superconducting critical temperature Tc is studied based on the time-dependent Ginzburg-Landau 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 γ1 proportional to the temperature measured from the critical point T−Tc, and the other is γ2 proportional to the excitation intensity of the pump pulse. The excited state approaches the equilibrium state exponentially in a long time t≫γ1−1, while in the intermediate-time domain we find a power-law or logarithmic decay with different exponents for t≪γ2−1 and γ2−1≪t≪γ1−1, 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.

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