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Q-MAC regular meeting 2020 has been cancelled. 

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Q-MAC Extension on the grounds of excellence

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Publication Detail / Abstract

P. E. Dolgirev, A. Zong, M. H. Michael, J. B. Curtis, D. Podolsky, A. Cavalleri, E. Demler

Periodic dynamics in superconductors induced by an impulsive optical quench

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A number of experiments have evidenced signatures of enhanced superconducting correlations after photoexcitation. Initially, these experiments were interpreted as resulting from quasi-static changes in the Hamiltonian parameters, for example, due to lattice deformations or melting of competing phases. Yet, several recent observations indicate that these conjectures are either incorrect or do not capture all the observed phenomena, which include reflection coefficient exceeding unity, large shifts of Josephson plasmon edges, and appearance of new peaks in terahertz reflectivity. These observations can be explained from a generic perspective of a periodic drive of system parameters. However, the origin of underlying oscillations remains unclear. In this paper, we demonstrate that oscillations at a well-defined frequency are generally expected in superconductors with low-energy Josephson plasmons following an incoherent pump. The origin of these oscillations is the parametric generation of plasmon pairs arising from pump-induced perturbation of the superconducting order parameter. We show that this bi-plasmon response can persist above the transition temperature as long as strong superconducting fluctuations are present. Our analysis applies to layered cuprate superconductors, with low-frequency c-axis plasmons, and isotropic materials such as K3C60, which also have a small plasmon gap. We discuss the relation of our findings to previously observed features of nonequilibrium superconductors and argue that bi-plasmons can be detected directly using currently available experimental techniques.
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