Thermal Fluctuations in d-wave Layered Superconductors

TL;DR

This paper investigates how thermal fluctuations affect the anisotropic d-wave order parameter in layered superconductors, predicting a quadratic temperature dependence of the c-axis penetration depth and comparing theoretical models with experimental data.

Contribution

It introduces a comprehensive analysis of thermal fluctuations in layered d-wave superconductors using the Lawrence-Doniach and extended t-J models, linking theory with experimental observations.

Findings

c-axis penetration depth exhibits quadratic temperature dependence at low temperatures

thermal fluctuations influence the orientation of the d-wave order parameter

model predictions align with conductance and specific heat measurements

Abstract

We study the thermal fluctuations of anisotropic order parameters (OP) in layered superconductors. In particular, for copper oxides and a d-wave OP, we present some experimental consequences of fluctuations in the direction normal to the layers. It is shown that the c-axis penetration depth $\lambda_c$ can have a "disorder-like" quadratic temperature dependence at low temperature. The fluctuations are analyzed in the framework of a Lawrence-Doniach model with an isotropic Fermi surface. Anisotropies pin the orientation of the OP to the crystallographic axes of the lattice. Then we study an extended t-J model that fits Fermi suface data of bilayers $YBCO$ and $BSCCO$. This leads to a d-wave OP with two possible orientations and, including the thermal fluctuations, yields the announced temperature dependence of $\lambda_c$. Furthermore a reservoir layer is introduced. It implies a finite density of states at the Fermi energy which is successfully compared to conductance and specific heat measurements.