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

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 φ-sweeps at various polar angles θ performed down to 0.1 K. Clear 4-fold oscillations of the specific heat and a rapid suppression of it by changing θ 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 γ-band with the lines of gap minima along the [100] directions, and the passive band is the α- and β-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 k_z direction.