ctd.qmat Team Deciphers Moiré Superconductivity

Overview

Writing in Nature, an international team of researchers has, for the first time, demonstrated a direct link between electronic states in quantum materials and moiré superconductivity. The theoretical framework was provided by a multi-site team from the Cluster of Excellence ctd.qmat.

How moiré superconductivity emerges is one of the central open questions in modern solid-state physics. Researchers from the Würzburg–Dresden Cluster of Excellence ctd.qmat — Complexity, Topology and Dynamics in Quantum Matter have now delivered the decisive theoretical explanation. Together with experimental verification, their results form the core component of a study recently published in Nature. These insights could one day pave the way for the development of new quantum materials and superconductors for future quantum technologies.

The theoretical work was carried out by Giorgio Sangiovanni, Principal Investigator and Professor of Computational Quantum Materials at ctd.qmat in Würzburg; Roser Valentí, Professor of Theoretical Solid-State Physics at Goethe University Frankfurt and a member of ctd.qmat’s Grete Hermann Network; Lorenzo Crippa, a former ctd.qmat postdoctoral researcher, now at the University of Hamburg; and colleagues from Princeton University. The experiments were carried out at the California Institute of Technology (Caltech).

A Slight Twist Gives Rise to a Novel Quantum State

The material under investigation consists of three atomically thin graphene layers stacked with a slight rotational misalignment. “When individual layers are overlaid with a relative twist of just about one degree, the well-known moiré effect emerges,” explains Giorgio Sangiovanni. This minute twist fundamentally alters electronic behavior: electron mobility within a single layer is reduced, while interactions across all three layers become dominant. This “electronic correlation” in turn leads to novel quantum states such as moiré superconductivity, in which electrons bind into Cooper pairs and move through the material without resistance.

Material Design Enables Superconductivity 

The key finding is this: moiré superconductivity does not arise in a conventional metal, but in a three-layer material system whose crystal lattices are each rotated ever so slightly with respect to one another. “Graphene is intrinsically a semiconductor,” says Roser Valentí. “Only when two or three graphene layers are stacked and gently twisted does it begin to behave like a strongly correlated metal — and ultimately become superconducting. Achieving this requires highly sophisticated material design.”