Pauli-paramagnetic effects on mixed state properties in a strongly anisotropic superconductor ---Application to Sr_2_RuO_4_---

TL;DR

This paper theoretically investigates the effects of Pauli paramagnetism on the mixed state properties of a strongly anisotropic superconductor, applying the findings to Sr2RuO4 to explain various experimental observations.

Contribution

It provides a quantitative theoretical analysis of Pauli paramagnetic effects on anisotropic superconductors and explains experimental phenomena in Sr2RuO4.

Findings

Explains the suppression of Hc2 for the ab plane direction.

Accounts for the larger anisotropy ratio and intensity in neutron scattering.

Reconciles the first order transition observed in various measurements.

Abstract

We study theoretically the mixed state properties of a strong uniaxially-anisotropic type II superconductor with the Pauli paramagnetic effect, focusing on their behaviors when the magnetic field orientation is tilted from the conduction layer ab plane. On the basis of Eilenberger theory, we quantitatively estimate significant contributions of the Pauli paramagnetic effects on a variety of physical observables, including transverse and longitudinal components of the flux line lattice form factors, magnetization curves, Sommerfeld coefficient, field distributions and magnetic torques. We apply these studies to Sr_2_RuO_4_ and quantitatively explain several seemingly curious behaviors, including the H_c2_ suppression for the ab plane direction, the larger anisotropy ratio and intensity found by the spin-flip small angle neutron scattering, and the first order transition observed recently in magneto-caloric, specific heat and magnetization measurements in a coherent and consistent manner. Those lead us to conclude that Sr_2_RuO_4_ is either a spin-singlet or a spin-triplet pairing with the d-vector components in the ab plane.