Superconductor–insulator transition in two-dimensional indium–indium-oxide composite

Abstract

The magnetic-field–tuned superconductor-to-insulator transition was studied in a hybrid system of superconducting indium islands, deposited on an indium oxide (InOx) thin film, which exhibits global superconductivity at low magnetic fields. Vacuum annealing was used to tune the conductivity of the InOx film, thereby tuning the inergrain coupling and the nature of the transition. The hybrid system exhibits a “giant” magnetoresistance above the magnetic-field–tuned superconductor-to-insulator transition (H-SIT), with critical behavior similar to that of uniform InOx films but at much lower magnetic fields, that manifests the duality between Cooper pairs and vortices. A key feature of this hybrid system is the separation between the quantum criticality and the onset of nonequilibrium behavior.

Overactivated transport in the localized phase of the superconductor-insulator transition

“…The x = 9% samples show a single activated behavior, while the x = 13.5% samples deviate from this law at the lowest temperatures. Previous works have reported such a behavior 15,19,20,[22][23][24]34 . It has often been referred to as overactivation and associated with the presence of superconductivity in the system 15,19,20,23,24 .…”

“…Previous works have reported such a behavior 15,19,20,[22][23][24]34 . It has often been referred to as overactivation and associated with the presence of superconductivity in the system 15,19,20,23,24 . However, this intriguing feature has mostly been observed under magnetic field 19,20,23,24,34 or pressure 22 , and has not been systematically addressed experimentally.…”

“…It has often been referred to as overactivation and associated with the presence of superconductivity in the system 15,19,20,23,24 . However, this intriguing feature has mostly been observed under magnetic field 19,20,23,24,34 or pressure 22 , and has not been systematically addressed experimentally. In particular, the role disorder plays in the emergence of this behavior has not yet been settled, neither has the nature of the excitations that are dominant for low frequency transport been determined.…”

“…Moreover, there is a controversy on whether the system is electronically homogeneous, granular, or fractal 6,14 . Especially intriguing are the reports of very strong insulating behaviors in the immediate vicinity of the SIT, with activated or even overactivated temperature dependence of the resistivity at the lowest experimentally accessible temperatures [15][16][17][18][19][20][21][22][23][24] . These findings have prompted fierce debate as to their possible interpretation.…”

Electron-Phonon Decoupling in Two Dimensions

“…Hence only materials with the Arrhenius resistivity at low temperatures could be potentially promising for detecting MBL. While the origin of a small Arrhenius gap, T 0 ∼ 1K, is quite an interesting problem by itself, we do not consider it here noticing only that there is a variety of materials with such a gap [20][21][22][23][24] which typically have granular disorder.…”