Highly crystalline 2D superconductors

TL;DR

This review discusses recent progress in highly-crystalline 2D superconductors, highlighting their unique quantum phenomena and potential for advancing quantum physics and superconductor research.

Contribution

It provides a comprehensive overview of recent developments and novel physical properties observed in highly-crystalline 2D superconductors, emphasizing their potential for new quantum physics exploration.

Findings

Observation of quantum metallic state in 2D superconductors

Detection of quantum Griffiths phase under magnetic fields

Superconductivity persisting in large in-plane magnetic fields

Abstract

Recent technological advances in controlling materials have developed methods to produce idealized two-dimensional (2D) electron systems such as heterogeneous interfaces, molecular-beam-epitaxy (MBE) grown atomic layers, exfoliated thin flakes and field-effect devices. These 2D electron systems are highly-crystalline with less disorder in common, some of which indeed show sheet resistance more than one order of magnitude lower even in atomic layers or single layers than that of conventional amorphous/granular thin films. Here, we present a review on the recent developments of highly-crystalline 2D superconductors and a series of unprecedented physical properties discovered in these systems. In particular, we highlight the quantum metallic state (or possible metallic ground state), the quantum Griffiths phase in out-of-plane magnetic fields, and the superconducting state maintained in anomalously large in-plane magnetic fields, which were observed in exfoliated 2D materials, MBE-grown atomic-layer thin films and electric-double-layer (ion-gated) interfaces. These phenomena are discussed on the basis of weakened disorder and/or broken spatial inversion symmetry. These novel aspects suggest that highly-crystalline 2D systems are promising platforms for exploring new quantum physics and superconductors.