Quantum coherence across bosonic superconductor-anomalous metal-insulator transitions

TL;DR

This study investigates quantum phase coherence across superconductor-metal-insulator transitions in high-Tc films, revealing an anomalous metallic state with saturated phase coherence that challenges traditional localization theories.

Contribution

It uncovers the evolution of quantum phase coherence across transitions and identifies a robust anomalous metallic state characterized by resistance and oscillation saturation at low temperatures.

Findings

Detection of an anomalous metallic state with saturated resistance and oscillation amplitude.

Monotonic growth of oscillation amplitude on the superconducting side with decreasing temperature.

Decrease of oscillation amplitude at low temperatures on the insulating side.

Abstract

After decades of explorations, suffering from low critical temperature and subtle nature, whether a metallic ground state exists in a two-dimensional system beyond Anderson localization is still a mystery. Supremely, phase coherence could be the key that unlocks its intriguing nature. This work reveals how quantum phase coherence evolves across bosonic superconductor-metal-insulator transitions via magneto-conductance quantum oscillations in high-Tc superconducting films. A robust intervening anomalous metallic state characterized by both resistance and oscillation amplitude saturations in the low temperature regime is detected. By contrast, with decreasing temperature the oscillation amplitude monotonically grows on the superconducting side, but decreases at low temperatures on the insulating side. It suggests that the saturation of phase coherence plays a prominent role in the formation of this anomalous metallic state.