Phenomenological theory of the superconducting state inside the hidden-order phase ofURu2Si2

Abstract

Recent experiments have unveiled important properties of the ground state of the elusive heavy fermion URu2Si2. While tetragonal symmetry-breaking was reported below the hidden-order (HO) transition at THO ≈ 17.5 K, time-reversal symmetry-breaking was observed below the superconducting transition temperature Tc < THO. Although the latter results have been used to argue in favor of a chiral d+id superconducting state, such an order parameter is incompatible with broken tetragonal symmetry. Here, we employ a phenomenological model to investigate the properties of a chiral superconducting state that develops inside the hidden-order phase. In this case, there are actually two superconducting transition temperatures: while Tc marks a normal-state to superconducting transition, T * c < Tc signals a superconducting-to-superconducting transition in which time-reversal symmetry is broken. In the phase T * c < T < Tc, the low-energy density of states ρ (ω) is enhanced due to the crossing of two nodal lines, giving rise to an unusual ω log(ω) dependence of ρ (ω), which is manifested in several thermodynamic properties. We also investigate the emergence of a soft amplitude gap mode near T * c . In contrast to the usual amplitude mode near a regular normal-state to superconducting transition, this mode becomes soft near a superconducting-to-superconducting transition, which in principle allows for its detection by Raman spectroscopy. Finally, we investigate the impact of twin domains on the anisotropic properties of the superconducting state, and propose experiments in mechanically strained samples to explore the interplay between hidden order and superconductivity in URu2Si2.

High-Dimensional Disorder-Driven Phenomena in Weyl Semimetals, Semiconductors, and Related Systems

“…(135) for review). A prominent example here is a the candidate d-wave superconductor U Ru2Si2 (136,137,138,139).…”

Polar Kerr effect studies of time reversal symmetry breaking states in heavy fermion superconductors

“…Observations of Pauli limiting behavior [82,83] pairing that harbors Weyl or double-Weyl fermions, respectively [94]. A third phenomenological study suggests that, as in UPt 3 , the real and imaginary components of the order parameter have different transition temperatures, with the hidden order acting as the symmetry-breaking field lifting the degeneracy between the two order parameter components [95]. However, in this case PKE would only accompany the lower of the two transitions.…”