Low-energy quasiparticle (QP) excitations in the heavy-fermion superconductor URu2Si2 were investigated by specific-heat C(T,H,φ,θ) 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(θ) measured under a rotating magnetic field within the ac plane exhibits a shoulder-like anomaly at θ ∼ 45° and a sharp dip at θ = 90° (H||a) in the moderate-field region. These features are supported by theoretical analyses based on microscopic calculations assuming the gap symmetry of kz(kx + iky), 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 URu2Si2 and have authenticated its chiral d-wave superconductivity.
ASJC Scopus subject areas
- Physics and Astronomy(all)