[Paper Review] Quantum coherence across bosonic superconductor-anomalous metal-insulator transitions

Chao Yang, Yi Liu+16 more|arXiv (Cornell University)|Jan 23, 2019

Physics of Superconductivity and Magnetism34 citations

TL;DR

The paper demonstrates how quantum phase coherence evolves across bosonic superconductor-metal-insulator transitions via magneto-conductance quantum oscillations in high-Tc superconducting films, revealing a robust anomalous metallic state with saturation in resistance and oscillation amplitude at low temperatures.

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.

Motivation & Objective

• Investigate whether a metallic ground state exists in a two-dimensional system beyond Anderson localization.
• Explore how quantum phase coherence evolves across bosonic S-M-I transitions.
• Characterize the anomalous metallic state and its dependence on temperature and magnetic field.

Proposed method

• Measure magneto-conductance and extract quantum oscillations in high-Tc superconducting films.
• Analyze temperature dependence of oscillation amplitude on both superconducting and insulating sides.
• Identify saturation behavior in resistance and oscillation amplitude at low temperature.
• Infer the role of phase coherence saturation in the formation of the anomalous metallic state.

Experimental results

Research questions

• RQ1 Does a metallic ground state exist in 2D systems beyond Anderson localization in these materials?
• RQ2 How does quantum phase coherence evolve across bosonic superconductor-metal-insulator transitions?
• RQ3 What is the role of phase coherence saturation in the anomalous metallic state?

Key findings

• A robust intervening anomalous metallic state is detected, characterized by saturation in both resistance and oscillation amplitude at low temperature.
• On the superconducting side, oscillation amplitude grows with decreasing temperature.
• On the insulating side, oscillation amplitude decreases at low temperatures.
• The saturation of phase coherence appears to play a prominent role in forming the anomalous metallic state.