Spectroscopic evidence of disorder-induced quantum phase transitions in monolayer Fe(Te,Se) superconductor

TL;DR

This study uses spectroscopic techniques to investigate how increasing disorder affects the quantum phase transition from superconducting to insulating states in a monolayer Fe(Te,Se) superconductor.

Contribution

It demonstrates controlled disorder introduction and observes spectral evolution, revealing disorder's role in quantum phase transitions in high-temperature 2D superconductors.

Findings

Spectral evolution from superconducting to insulating gaps with increased disorder.

Observation of large U-shaped gaps at strong disorder, linked to localization-enhanced Cooper pairing.

Insights into emergent phases in low-dimensional high-temperature superconductors with disorder.

Abstract

The superconductor-insulator transition as a paradigm of quantum phase transitions has attracted tremendous interest over the past three decades. While the magnetic field and carrier density can be tuned to drive the transition, the role of disorder in the transition is not well understood due to the complicated interplay between superconductivity and electron localization. In this work, we controllably introduce disorder in a two-dimensional high-temperature superconductor by depositing iron clusters onto the superconducting monolayer Fe(Te,Se) crystalline film. The spectral evolution from superconducting gaps to insulating gaps with increasing disorder is detected by scanning tunneling spectroscopy measurements. When the disorder is strong, large U-shaped gaps are observed and attributed to the localization-enhanced Cooper pair correlation. Our observations provide the insight into the emergent phases of low-dimensional and high-temperature superconductors with disorder.