Interplay between effective mass anisotropy and Pauli paramagnetic effects in a multiband superconductor--Application to Sr2RuO4--

Abstract

We investigate the mixed state properties in a type II multiband superconductor with uniaxial anisotropy under the Pauli paramagnetic effects. Eilenberger theory extended to a multiband superconductor is utilized to describe the detailed vortex lattice properties, such as the flux line form factors, the vortex lattice anisotropy and magnetic torques. We apply this theory to Sr${}_2$RuO${}_4$ to analyze those physical quantities obtained experimentally, focusing on the interplay between the strong two-dimensional anisotropy and the Pauli paramagnetic effects. This study allows us to understand the origin of the disparity between the vortex lattice anisotropy ($\sim$60) and the $H_{c2}$ anisotropy ($\sim$20). Among the three bands; $\gamma$ with the effective mass anisotropy $\sim$180, $\alpha$ with $\sim$120, and $\beta$ with $\sim$60, the last one is found to be the major band, responsible for various magnetic responses while the minor $\gamma$ band plays an important role in the vortex formation. Namely, in a field orientation slightly tilted away from the two dimensional basal plane those two bands cooperatively form the optimal vortex anisotropy which exceeds that given by the effective mass formula with infinite anisotropy. This is observed by small angle neutron scattering experiments on Sr${}_2$RuO${}_4$. The pairing symmetry of Sr${}_2$RuO${}_4$ realized is either spin singlet or spin triplet with the d-vector strongly locked in the basal plane. The gap structure is that the major $\beta$ band has a full gap and the minor $\gamma$ band has a $d_{x^2-y^2}$ like gap.

14 pages, 18 figures, to appear in Phys. Rev. B

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Cited by in corpus (8)

• Symmetry Protected Topological Superfluids and Superconductors --- From the Basics to ${}^3$He ---
• Possible three-dimensional nematic odd-parity superconductivity in Sr${}_2$RuO${}_4$
• Superconducting pairing in Sr${}_2$RuO${}_4$ from weak to intermediate coupling
• Anisotropy and multiband superconductivity in Sr2RuO4
• Simultaneous Evidence for Pauli Paramagnetic Effects and Multiband Superconductivity in KFe${}_2$As${}_2$ by Small-Angle Neutron Scattering Studies of the Vortex Lattice
• Microscopic Eilenberger theory of Fulde-Ferrell-Larkin-Ovchinnikov states in the presence of vortices
• Theoretical studies for identifying horizontal line nodes via angle-resolved density of states measurements ---Application to Sr${}_2$RuO${}_4$---
• High-resolution magnetostriction measurements of the Pauli-limited superconductor Sr2RuO4