Voltage-tuned anomalous-metal to metal transition in hybrid Josephson junction arrays

TL;DR

This study demonstrates voltage-controlled phase transitions in hybrid Josephson junction arrays, revealing an anomalous metallic phase that emerges between superconducting and insulating states and can be tuned via electrostatic gating.

Contribution

The paper introduces a novel device design with independent electrostatic tuning, enabling exploration of multiple phase transitions and the discovery of an anomalous metallic phase in Josephson junction arrays.

Findings

Identification of an anomalous metallic phase with saturating resistivity.

Continuous tuning of the metallic regime over three orders of magnitude in resistivity.

Suppression of the anomalous metallic phase by magnetic frustration.

Abstract

We report voltage-tuned phase transitions in arrays of hybrid semiconductor-superconductor islands arranged in a square lattice. A double-layer electrostatic gate geometry enables independent tuning of inter-island coupling and proximity-induced superconductivity. This design enables access to the superconductor-insulator, superconductor-metal, and metal-insulator transitions in a single device, revealing critical points and emergent intermediate phases. We find that the superconductor-insulator transition is interrupted by an anomalous metallic phase with saturating low-temperature resistivity. Across gate voltages, this regime extends over three orders of magnitude in resistivity and can be continuously tuned into the conventional metallic phase. The signature of the anomalous metallic phase is suppressed by magnetic frustration.