Extreme Sensitivity of the Superconducting State in Thin Films

TL;DR

This study reveals that thin-film superconductors are highly sensitive to external radiation, which can suppress superconductivity and induce a metallic state, highlighting the fragile nature of 2D superconductivity.

Contribution

It demonstrates the extreme sensitivity of 2D superconducting films to external perturbations and links this to their marginal stability in two dimensions.

Findings

External radiation filtering eliminates the metallic state.

Superconducting films show temperature-independent metallic transport.

Superconductivity in 2D is only marginally stable.

Abstract

All non-interacting two-dimensional electronic systems are expected to exhibit an insulating ground state. This conspicuous absence of the metallic phase has been challenged only in the case of low-disorder, low density, semiconducting systems where strong interactions dominate the electronic state. Unexpectedly, over the last two decades, there have been multiple reports on the observation of a state with metallic characteristics on a variety of thin-film superconductors. To date, no theoretical explanation has been able to fully capture the existence of such a state for the large variety of superconductors exhibiting it. Here we show that for two very different thin-film superconductors, amorphous indium-oxide and a single-crystal of 2H-NbSe2, this metallic state can be eliminated by filtering external radiation. Our results show that these superconducting films are extremely sensitive to external perturbations leading to the suppression of superconductivity and the appearance of temperature independent, metallic like, transport at low temperatures. We relate the extreme sensitivity to the theoretical observation that, in two-dimensions, superconductivity is only marginally stable.