Dissipative phases across the superconductor-to-insulator transition

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Phenomena

Background:

• Low-dimensional systems exhibit exotic electronic phases driven by symmetry breaking or topology.
• The interplay of superfluidity, disorder, and interactions in two-dimensional (2D) systems is crucial but not fully understood.
• Theory predicts a direct superconductor-to-insulator transition, with no metallic state surviving disorder in 2D.

Purpose of the Study:

• To investigate the phase diagram of amorphous niobium-silicon (NbSi) thin films.
• To explore the influence of disorder and film thickness on electronic phases.
• To understand the nature of metallic states emerging in the vicinity of the superconducting-insulating transition.

Main Methods:

• Fabrication and characterization of amorphous NbSi thin films.
• Systematic variation of disorder and film thickness.
• Measurement of electrical resistance as a function of temperature and disorder.

Main Results:

• Identified two distinct metallic phases between the superconducting and insulating states.
• These metallic phases are dissipative, with resistance extrapolating to a finite value at zero temperature.
• Observed specific disorder dependencies for each metallic phase, suggesting inhomogeneous superconductivity destruction.

Conclusions:

• The existence of these metallic phases challenges the conventional understanding of the superconductor-to-insulator transition in 2D.
• The results suggest that superconducting fluctuations can stabilize metallic states that are not predicted by current theories.
• Inhomogeneity in superconductivity destruction, even in morphologically uniform films, likely drives these exotic metallic phases.