Two-dimensional superconductivity in a thick exfoliated kagome film

TL;DR

This paper demonstrates two-dimensional superconductivity in thick exfoliated kagome CsV$_3$Sb$_5$ films, revealing BKT transition behavior and exceeding Pauli limits, linking charge density waves with superconductivity.

Contribution

It provides the first evidence of 2D superconductivity in thick kagome films, with detailed analysis of critical fields and transition behaviors, advancing understanding of 2D SC in complex materials.

Findings

Observation of BKT transition in thick films

Superconductivity exceeds Pauli paramagnetic limit

Correlation between charge density waves and superconductivity

Abstract

We report the observation of two-dimensional superconductivity (2D SC) in exfoliated kagome metal CsV$_3$Sb$_5$ with a thickness far thicker than the atomic limit. By examining the critical current and upper critical magnetic fields ($H_{c2}$) of 40-60 nm thick films in the superconducting state, we identify a pronounced Berezinskii-Kosterlitz-Thouless (BKT) transition behavior, i.e. a drastic decrease of the superfluid stiffness near the transition, and a cusp-like feature of the angular dependent $H_{c2}$, both of which serve as direct evidence of 2D SC. In addition, an exceeding of the Pauli paramagnetic limit of the in-plane $H_{c2}$ is consistent with the 2D SC nature. The observed 2D SC occurs in thick films with the highest superconducting transition temperature $T_c$ and the lowest charge density wave transition temperature $T_{\rm {CDW}}$, which suggests that the charge density wave states are interrelated with the superconducting states. Our findings impose constraints in understanding the enhancement of SC in kagome superconductors, and illuminate pathways for achieving novel 2D superconducting states in more stable and much thicker systems.