Determination of the Superconducting Gap Structure in All Bands of the Spin-Triplet Superconductor Sr2RuO4

TL;DR

This study provides comprehensive experimental evidence for the full superconducting gap structure in all three bands of Sr2RuO4, revealing detailed anisotropies and the active/passive band roles in its spin-triplet superconductivity.

Contribution

First to determine the complete gap structure in all bands of Sr2RuO4 using advanced field-orientation specific heat measurements.

Findings

Active gamma-band has gap minima along [100] directions.

Passive alpha- and beta-bands have minima or zeros along [110] directions.

Supports line-node-like gaps along the kz direction.

Abstract

We have obtained strong experimental evidence for the full determination of the superconducting gap structure in all three bands of the spin-triplet superconductor Sr2RuO4 for the first time. We have extended the measurements of the field-orientation dependent specific heat to include conical field rotations consisting of in-plane azimuthal angle phi-sweeps at various polar angles theta performed down to 0.1 K. Clear 4-fold oscillations of the specific heat and a rapid suppression of it by changing theta are explained only by a compensation from two types of bands with anti-phase gap anisotropies with each other. The results indicate that the active band, responsible for the superconducting instability, is the gamma-band with the lines of gap minima along the [100] directions, and the passive band is the alpha- and beta-bands with the lines of gap minima or zeros along the [110] directions in their induced superconducting gaps. We also demonstrated the scaling of the specific heat for the field in the c-direction, which supports the line-node-like gap structures running along the kz direction.