Intermediate bosonic metallic state in the superconductor-insulator transition

Area of Science:

• Condensed Matter Physics
• Quantum Materials Science
• Low-Temperature Physics

Background:

• The existence of a metallic ground state in two-dimensional systems beyond Anderson localization is a long-standing theoretical and experimental challenge.
• Understanding the interplay between superconductivity, metallic behavior, and insulating states is crucial for advancing quantum electronics.

Purpose of the Study:

• To investigate the nature of quantum phase coherence across superconductor-metal-insulator transitions in two-dimensional systems.
• To identify and characterize any intervening metallic states and their relationship to phase coherence.

Main Methods:

• Utilized magnetoconductance quantum oscillations to probe quantum phase coherence.
• Studied nanopatterned high-temperature superconducting films, tuning phase coherence by varying etching time.
• Analyzed resistance and oscillation amplitude at low temperatures to identify distinct electronic regimes.

Main Results:

• Detected a robust anomalous metallic state between the superconducting and insulating regimes.
• Observed saturating resistance and oscillation amplitude in this metallic state at low temperatures.
• Evidence suggests this anomalous metallic state is bosonic in nature.

Conclusions:

• The saturation of quantum phase coherence plays a significant role in the formation of the anomalous metallic state.
• This finding provides new insights into the complex phase diagrams of two-dimensional electron systems.
• Challenges conventional understanding of electron localization and metallic behavior in reduced dimensions.