Plane - Chain coupling in YBa_{2}Cu_{3}O_{7} : temperature dependence of the penetration depth

TL;DR

This paper models the temperature-dependent penetration depth in YBa2Cu3O7 by considering pairing in CuO2 planes and chains, successfully explaining anisotropy and low-temperature behavior.

Contribution

It introduces a coupled plane-chain model with Coulomb interactions that reproduces the anisotropic penetration depth and its temperature dependence in YBa2Cu3O7.

Findings

Model accounts for anisotropy of penetration depth

Reproduces temperature dependence including low-temperature linearity

Parameters used are physically reasonable

Abstract

We have studied the penetration depth for a model of $YBa_{2}Cu_{3}O_{7}$ involving pairing both in the $CuO_{2}$ planes and in the CuO chains. In this model pairing in the planes is due to an attractive interaction, while Coulomb repulsion induces in the chains an order parameter with opposite sign. Due to the anticrossing produced by hybridization between planes and chains, one obtains a d-wave like order parameter which changes sign on a single sheet of the Fermi surface and has nodes in the gap. We find that our model accounts quite well for the anisotropy of the penetration depth and for the absolute values. We reproduce fairly well the whole temperature dependence for both the a and the b directions, including the linear dependence at low temperature. We use a set of parameters which are all quite reasonable physically. Our results for the c direction are also satisfactory, although the situation is less clear both experimentally and theoretically.