Clean-Limit 2D Superconductivity in a Thick Exfoliated Kagome Film

Abstract

The presence of superconductivity (SC) in low-dimensional, clean-limit systems gives rise to abundant exotic quantum properties and provides an ideal platform for advanced device applications. Reduced dimensionality modifies SC and enables topological phases, while clean-limit systems promise a pathway to utilizing electronic/spintronic devices with enhanced performance. However, achieving clean-limit 2D SC remains challenging due to the inherent fragility of ultrathin films. Here, clean-limit 2D SC in a thick exfoliated film of the kagome metal CsV₃Sb₅ is unambiguously observed. By systematically investigating the transport properties, two lines of direct evidence are identified: 1) a drastic decrease in superfluid stiffness near the superconducting transition; 2) a cusp-like feature in the angular dependence of the upper critical field (H_c2). Additionally, the observation of in-plane H_c2 exceeding the Pauli paramagnetic limit confirms the 2D nature of the SC. The clean-limit nature of the 2D SC establishes CsV₃Sb₅ as an ideal candidate for fabricating robust superconducting devices with non-dissipative vortex motion. Furthermore, the interplay between SC and charge-density-wave ordering is analyzed, illuminating pathways for identifying systems with similar robust low-dimensional quantum properties. The findings therefore offer guiding principles for the design of new materials and devices optimized for enhanced superconducting performance and stability.