Abstract
URu2Si2 is a promising candidate for a chiral d-wave superconductor whose gap is composed of a horizontal line node at equator and point nodes at the north and south poles. However, previous measurements of the specific heat and the thermal conductivity did not detect quasiparticle excitations from a horizontal line node in heavy-mass bands. Here, we have provided strong evidence for the presence of a horizontal line node from field-angle-dependent specific-heat measurements by using a high-quality single crystal of URu2Si2. We observed the behavior of the specific heat at low fields which does not depend on inplane field angle ϕ but shows a shoulder-like anomaly in the polar-angle θ dependence around θ ∼ 45°. This feature is more clearly seen at lower temperatures, suggesting the detection of low-energy quasiparticle excitations reflecting the gap structure. From theoretical analyses based on microscopic calculations, we have demonstrated that this anomaly can be explained by the existence of a horizontal line node at kz = 0. Thus, the gap structure of URu2Si2 matches well with the Eg chiral kz(kx + iky) symmetry.
Highlights
URu2 Si2 exhibits unconventional superconductivity below Tc = 1.4 K in the mysterious “hidden order” phase
Broken time reversal symmetry in the superconducting state has been suggested from recent polar Kerr-effect measurements [6]
In order to settle this controversy on the gap structure of URu2 Si2, we have performed fieldangle-dependent specific-heat measurements at low temperatures by using a high-quality single crystal [10]
Summary
In order to settle this controversy on the gap structure of URu2 Si2 , we have performed fieldangle-dependent specific-heat measurements at low temperatures by using a high-quality single crystal [10] In this contribution, we report the field-angle φ and θ dependence of the H behavior in the specific heat, evidencing the presence of a horizontal line node in heavy-mass bands at kz = 0. We report the field-angle φ and θ dependence of the H behavior in the specific heat, evidencing the presence of a horizontal line node in heavy-mass bands at kz = 0 These results ensure that the gap symmetry of URu2 Si2 is of the kz (kx + iky ) type
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