Hot Electron Effects in the 2D Superconductor-Insulator Transition

TL;DR

This study investigates the superconductor-insulator transition in ultrathin amorphous Bi films, revealing that apparent metallic behavior at low temperatures results from electron heating effects rather than intrinsic properties.

Contribution

It demonstrates that the temperature-independent resistance regime is due to electron heating, challenging the interpretation of a true metallic phase in 2D superconductor-insulator transitions.

Findings

Resistance is temperature-independent below 120 mK due to electron heating.

Electric field scaling can be related to electron temperature, not intrinsic critical behavior.

Electron heating effects obscure the true nature of the transition.

Abstract

The parallel magnetic field tuned two-dimensional superconductor-insulator transition has been investigated in ultrathin films of amorphous Bi. The resistance is found to be independent of temperature on both sides of the transition below approximately 120 mK. Several observations suggest that this regime is not intrinsically "metallic" but results from the failure of the films' electrons to cool. The onset of this temperature-independent regime can be moved to higher temperatures by either increasing the measuring current or the level of electromagnetic noise. Temperature scaling is successful above 120 mK. Electric field scaling can be mapped onto temperature scaling by relating the electric fields to elevated electron temperatures. These results cast doubt on the existence of an intrinsic metallic regime and on the independent determination of the correlation length and dynamical critical exponents obtained by combining the results of electric field and temperature scaling.