Angular dependence of the upper critical field of Sr2RuO4

TL;DR

This study investigates how the upper critical magnetic field in Sr2RuO4 varies with angle and temperature, revealing limits at low temperatures and near Tc, which could shed light on its unconventional superconductivity.

Contribution

It provides a detailed angular and temperature dependence of Hc2 in Sr2RuO4, highlighting limits at low temperatures and near Tc, and introduces an effective-mass model with temperature-dependent anisotropy.

Findings

Hc2 is limited at low temperatures for angles less than 5 degrees.

The Hc2 limit persists near the critical temperature.

An anisotropic effective-mass model with temperature-dependent anisotropy better explains the data.

Abstract

One of the remaining issues concerning the spin-triplet superconductivity of Sr2RuO4 is the strong limit of the in-plane upper critical field Hc2 at low temperatures. In this study, we clarified the dependence of Hc2 on the angle theta between the magnetic field and the ab plane at various temperatures, by precisely and accurately controlling the magnetic field direction. We revealed that, although the temperature dependence of Hc2 for |theta| > 5 is well explained by the orbital pair-breaking effect, Hc2(T) for |theta| < 5 is clearly limited at low temperatures. We also revealed that the Hc2 limit for |theta| < 5 is present not only at low temperatures, but also at temperatures close to Tc. These features may provide additional hints for clarifying the origin of the Hc2 limit. Interestingly, if the anisotropic ratio in Sr2RuO4 is assumed to depend on temperature, the observed angular dependence of Hc2 is reproduced better at lower temperature with an effective-mass model for an anisotropic three-dimensional superconductor. We discuss the observed behavior of Hc2 based on existing theories.