Competition between anisotropy and superconductivity in organic and cuprate superconductors

TL;DR

This paper investigates the relationship between penetration depth and conductivity in quasi-2D superconductors, revealing the importance of three-dimensional effects and quantum criticality in understanding superconductivity in cuprates and organics.

Contribution

It applies scaling theory to analyze empirical data, demonstrating the 3D nature of superconductivity and the influence of quantum critical points in organic and cuprate superconductors.

Findings

Superconductivity is a genuine 3D phenomenon in these materials.

Competition between anisotropy and superconductivity suppresses superconductivity in 2D limit.

Data indicates flow to quantum criticality, including 2D-QSI and 3D-QSN transitions.

Abstract

We analyze the empirical correlation between the zero temperature penetration depth $\lambda_{c}(0) $ and the corresponding normal state DC conductivity $\sigma_{c}^{DC}$, measured slightly above the transition temperature $T_{c}$, in different classes of quasi two-dimensional superconductors, including cuprates and organics. For this purpose we invoke the scaling theory of quantum and finite temperature critical phenomena. Important implications are: Superconductivity in the organic and cuprate superconductors is a genuine three dimensional (3D) phenomenon. The competition between anisotropy and superconductivity destroys the latter in the 2D limit even in the ground state. The data uncovers the flow to quantum criticality, including the 2D quantum superconductor to insulator (2D-QSI) and the 3D quantum superconductor to normal state (3D-QSN) transition. This flow gives a clear perspective of the regimes where quantum fluctuations are essential and mean-field treatments fail. Thus, a detailed account of the flow from mean-field to 2D-QSI criticality in organics and the crossover from the 2D-QSI to the 3D-QSN critical point in cuprates is a challenge for microscopic theories attempting to solve the puzzle of superconductivity in these materials.