Thermodynamic parameters of atomically thin superconductors derived from the upper critical field

TL;DR

This paper introduces a new method to determine fundamental superconducting parameters in atomically thin materials using upper critical field measurements, providing insights into their pairing mechanisms and enhancing understanding of 2D superconductors.

Contribution

A novel approach to extract superconducting energy gap and specific heat jump from upper critical field data in atomically thin superconductors.

Findings

Parameters match expected values for strong- and moderately strong-coupled superconductors.

Enhanced in-plane critical field explained by sample geometry, not exotic pairing.

Method applicable to various 2D superconducting materials.

Abstract

The amplitude of ground state superconducting energy gap $\Delta(0)$ and relative jump in electronic specific heat at the transition temperature, $\Delta$$C$${/}$$\gamma$$T_c$, are primary fundamental parameters of any superconductor. There are several well-established techniques to measure these values for bulk samples. However, there is limited number of techniques which can be applied to measure these parameters in atomically thin superconductors. Here we proposed a new approach to extract $\Delta(0)$ and $\Delta$$C$${/}$$\gamma$$T_c$ in atomically thin superconductors by utilizing perpendicular, Bc2,perp(T) (when magnetic field is applied in perpendicular direction to the film surface), and parallel, Bc2,||(T) (when magnetic field is applied in parallel direction to the film surface), upper critical field data. Deduced parameters for few layers thick Al, Sn, NbSe2, MoS2, magic angle twisted trilayer graphene (MATTG), and WTe2 are well matched values expected for strong- and moderately strong-coupled electron-phonon mediated superconductors. Observed, in many atomically thin superconductors, an enhancement of Bc2,||(0) above the Pauli-Clogston-Chandrasekhar limiting field (i.e., magnetic field required to break the Cooper pair) is explained based on the sample geometry, without an assumption that some exotic pairing mechanism, for instance, Ising-type, is emergent in these materials.