In-plane upper critical field anisotropy in Sr2RuO4 and CeIrIn5

摘要

Experiments on tetragonal Sr2RuO4 and CeIrIn5 indicate the presence ofsuperconductivity with a multi-component superconducting order parameter. Suchan order parameter should exhibit an in-plane anisotropy in the upper criticalfield near the superconducting transition temperature that does not occur forsingle-component superconductors. Here, this anisotropy is determined frommicroscopic calculations for arbitrary gap functions. It is shown that thisanisotropy is generally not small and, in some cases, independent of impurityscattering. Furthermore, this anisotropy is calculated for many detailedmicroscopic models of Sr2RuO4. For these models this anisotropy is found to belarge, which is in sharp contrast to the small anisotropy observedexperimentally. However, an accidental cancellation of the anisotropy for gapson different Fermi surface sheets can lead to a result that is consistent withexperiment.