a-b Plane Anisotropy in YBCO

TL;DR

This paper investigates the anisotropic penetration depth in YBCO, revealing significant in-plane anisotropy and challenging simple d-wave models, thus supporting more complex three-dimensional theories with interplane interactions.

Contribution

It provides experimental evidence of in-plane anisotropy in YBCO's penetration depth and discusses implications for theoretical models of superconductivity.

Findings

High anisotropy in zero-temperature in-plane penetration depth.

Similar temperature dependence of lambda_a(T) and lambda_b(T).

Supports three-dimensional models with interplane interactions.

Abstract

The zero temperature in plane penetration depth in an untwinned single crystal of optimally doped YBa_2Cu_3O_6.93 is highly anisotropic. This fact has been interpreted as evidence that a large amount of the condensate resides in the chains. On the other hand, the temperature dependence of lambda_a(T)/lambda_a(0) and lambda_b(T)/lambda_b(0) (where the b-direction is along the chains) are not very different. This constrains theories and is, in particular, difficult to understand within a proximity model with d-wave pairing only in the CuO_2 plane and none on the CuO chains but instead supports a more three dimensional models with interplane interactions.