Possible Eliashberg-type superconductivity enhancement effects in a two-band superconductor MgB2 driven by narrow-band THz pulses

TL;DR

This study investigates how narrow-band THz pulses can enhance superconductivity in MgB2 by inducing non-thermal quasiparticle distributions, revealing a novel Eliashberg-type enhancement effect that competes with pair-breaking.

Contribution

It demonstrates that narrow-band THz pulses can induce an Eliashberg-type enhancement of superconductivity in a two-band superconductor, a phenomenon not previously observed with optical excitation.

Findings

Reduced pair-breaking efficiency near 0.7 T_c with THz pulses

Long-lived non-thermal quasiparticle distributions observed

Evidence of Eliashberg-type superconductivity enhancement

Abstract

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.