Continuous and reversible tuning of the disorder-driven superconductor-insulator transition in bilayer graphene

TL;DR

This study demonstrates precise, reversible control of the superconductor-insulator transition in bilayer graphene by tuning disorder, revealing a crossover from classical to quantum percolation through electrical gating.

Contribution

It introduces an experimental method for in-situ, reversible tuning of disorder in bilayer graphene to study the superconductor-insulator transition with detailed control.

Findings

Electrical gating induces percolative superconducting clusters.

Scaling behavior aligns with classical percolation.

Observation of a crossover from classical to quantum percolation.

Abstract

The influence of static disorder on a quantum phase transition (QPT) is a fundamental issue in condensed matter physics. As a prototypical example of a disorder-tuned QPT, the superconductor-insulator transition (SIT) has been investigated intensively over the past three decades, but as yet without a general consensus on its nature. A key element is good control of disorder. Here, we present an experimental study of the SIT based on precise in-situ tuning of disorder in dual-gated bilayer graphene proximity-coupled to two superconducting electrodes through electrical and reversible control of the band gap and the charge carrier density. In the presence of a static disorder potential, Andreev-paired carriers formed close to the Fermi level in bilayer graphene constitute a randomly distributed network of proximity-induced superconducting puddles. The landscape of the network was easily tuned by electrical gating to induce percolative clusters at the onset of superconductivity. This is evidenced by scaling behavior consistent with the classical percolation in transport measurements. At lower temperatures, the solely electrical tuning of the disorder-induced landscape enables us to observe, for the first time, a crossover from classical to quantum percolation in a single device, which elucidates how thermal dephasing engages in separating the two regimes.