Non-equilibrium phenomena in superconductors probed by femtosecond time-domain spectroscopy
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Abstract
Development of ultrafast lasers and nonlinear optical techniques over the last two decades provides tools to access real-time dynamics of low energy excitations in superconductors. For example, time-resolved THz spectroscopy and time- and angular-resolved photoemission spectroscopy provide access to the real-time dynamics of the superconducting gap amplitude. Such studies enable determination of microscopic parameters like quasi-particle recombination rates, pair-breaking rates and electron–boson coupling constants. Recently, intense THz pulses have been used to probe the nonlinear dynamics, including observation of collective modes. Moreover, using low-frequency electromagnetic pulses, there are several reports of amplification of superconductivity in both conventional and unconventional superconductors. Starting with a brief historical overview of the pioneering work, where non-equilibrium phenomena in superconductors were investigated using quasi-continuous excitation, we review some of the insights that are provided by using real-time approaches. We focus on conventional BCS superconductors, whose ground state is reasonably well understood, and address similarities and open questions related to the corresponding studies in high-𝑇𝑐
T
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superconductors.
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Journal of low temperature physics, 201, Springer Science + Business Media B.V., Dordrecht, 2020, https://doi.org/10.1007/s10909-020-02461-y