Optical study of superconducting Ga-rich layers in silicon

TL;DR

This study investigates superconducting Ga-rich layers in silicon using terahertz spectroscopy, revealing a conventional superconducting energy gap and strong electron-phonon coupling consistent with an amorphous Ga state.

Contribution

First optical measurement of superconducting Ga-rich layers in silicon, demonstrating their properties align with conventional superconductors and strong electron-phonon interactions.

Findings

Superconducting transition temperature T_c = 6.7 K.

Energy gap 2Δ(0) = 2.64 meV and ratio 4.6.

Terahertz spectra fit Eliashberg theory with strong coupling.

Abstract

We performed phase-sensitive terahertz (0.12 - 1.2 THz) transmission measurements of Ga-enriched layers in silicon. Below the superconducting transition, T_{c} = 6.7 K, we find clear signatures of the formation of a superconducting condensate and of the opening of an energy gap in the optical spectra. The London penetration depth, \lambda(T), and the condensate density, n_{s} = \lambda^{2} 0)/\lambda^{2}(T), as functions of temperature demonstrate behavior, typical for conventional superconductors with \lambda(0) = 1.8 \mu m. The terahertz spectra can be well described within the framework of Eliashberg theory with strong electron-phonon coupling: the zero-temperature energy gap is 2\Delta(0) = 2.64 meV and 2\Delta(0)/k_{B}T_{c} = 4.6 \pm 0.1, consistent with the amorphous state of Ga. At temperatures just above T_{c}, the optical spectra demonstrate Drude behavior.