paper

Evidence for chiral d-wave superconductivity in URu2Si2 from the field-angle variation of its specific heat

arXiv:1511.06060 · doi:10.7566/JPSJ.85.033704

Abstract

Low-energy quasiparticle (QP) excitations in the heavy-fermion superconductor URu $_{2}$ Si $_{2}$ were investigated by specific-heat $C (T, H, I ¨ , I^¸)$ measurements of a high-quality single crystal. The occurrence of QP excitations due to the Doppler-shift effect was detected regardless of the field direction in $C (H)$ of the present clean sample, which is in sharp contrast to a previous report. Furthermore, the polar-angle-dependent $C (I^¸)$ measured under a rotating magnetic field within the ac plane exhibits a shoulder-like anomaly at $I^¸ \sim 45$ deg and a sharp dip at $I^¸ = 90$ deg ( $H ∥ a$ ) in the moderate-field region. These features are supported by theoretical analyses based on microscopic calculations assuming the gap symmetry of $k_{z} (k_{x} + i k_{y})$ , whose gap structure is characterized by a combination of a horizontal line node at the equator and point nodes at the poles. The present results have settled the previous controversy over the gap structure of URu $_{2}$ Si $_{2}$ and have authenticated its chiral $d$ -wave superconductivity.

4 pages, 4 figures, published in J. Phys. Soc. Jpn