Quantum criticality and tunable Griffiths phase in superconducting twisted trilayer graphene

TL;DR

This paper reports the discovery of a magnetic field-tuned superconductor-insulator transition in twisted trilayer graphene, revealing a broad quantum Griffiths phase with unique critical behavior and local superconducting regions.

Contribution

It provides the first experimental evidence of a quantum Griffiths phase and tunable quantum criticality in twisted trilayer graphene, demonstrating control over disorder-induced quantum phenomena.

Findings

Observation of a broad quantum Griffiths phase in TTG

Detection of a reentrant transition from insulating to superconducting transport

Strong violation of the Pauli limit in TTG

Abstract

When dimensionality is reduced, enhanced quantum fluctuations can destroy long-range phase coherence, driving a superconductor insulator transition, SIT, where disorder and electronic correlations give rise to novel many-body states. Here, we report the first observation of a magnetic field tuned SIT in mirrorsymmetric twisted trilayer graphene, TTG. Remarkably, signatures of quantum criticality persist over an exceptionally broad range of magnetic fields and are well described by the formation of a quantum Griffiths phase, a regime in which rare spatially extended regions develop local order within a globally disordered phase. This leads to a quantum phase transition governed by an infinite-randomness fixed point and characterized by ultraslow relaxation dynamics. Near the quantum critical region, transport measurements reveal strongly nonlinear electrical behavior, including a current-driven reentrant transition from insulating to superconducting transport, providing direct evidence of local superconducting order. By tilting the magnetic field, we are able to collapse the broad Griffiths regime into a single quantum critical point, QCP, demonstrating a striking level of control over disorder induced quantum dynamics. Our results further show that TTG strongly violates the Pauli limit and establishes twisted trilayer graphene as a tunable platform for exploring quantum phase fluctuations, Cooper pair localization, and unconventional superconductivity.