We study THz-driven condensate dynamics in epitaxial thin films of MgB$_{ 2}$, a prototype two-band superconductor (SC) with weak interband coupling. The temperature and excitation density dependent dynamics follow the behavior predicted by the phenomenological bottleneck model for the single-gap SC, implying adiabatic coupling between the two condensates on the ps timescale. The amplitude of the THz-driven suppression of condensate density reveals an unexpected decrease in pair-breaking efficiency with increasing temperature - unlike in the case of optical excitation. The reduced pair-breaking efficiency of narrow-band THz pulses, displaying minimum near $\approx0.7$ T$_{ c}$, is attributed to THz-driven, long-lived, non-thermal quasiparticle distribution, resulting in Eliashberg-type enhancement of superconductivity, competing with pair-breaking.
Categories: cond-mat.supr-con cond-mat.mtrl-sci cond-mat.str-el