Twofold Spontaneous Symmetry Breaking in the Heavy-Fermion Superconductor UPt3

Department of Physics, Tokyo Institute of Technology, Meguro 152-8551, Japan.
Physical Review Letters (Impact Factor: 7.51). 04/2012; 108(15):157002. DOI: 10.1103/PhysRevLett.108.157002
Source: PubMed


The field-orientation dependent thermal conductivity of the heavy-fermion superconductor UPt3 was measured down to very low temperatures and under magnetic fields throughout the distinct superconducting phases: B and C phases. In the C phase, a striking twofold oscillation of the thermal conductivity within the basal plane is resolved reflecting the superconducting gap structure with a line of node along the a axis. Moreover, we find an abrupt vanishing of the oscillation across a transition to the B phase, as a clear indication of a change of gap symmetries. We also identify extra two line nodes below and above the equator in both B and C phases. From these results together with the symmetry consideration, the gap function of UPt3 is determined as a E(1u) representation characterized by a combination of two line nodes at the tropics and point nodes at the poles.

Full-text preview

Available from: ArXiv
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Motivated by a recent angle-resolved thermal conductivity experiment that shows a twofold gap symmetry in the high-field and low-temperature C phase in the heavy-fermion superconductor UPt$_3$, we group-theoretically identify the pairing functions as $E_{1u}$ with the $f$-wave character for all the three phases. The pairing functions are consistent with the observation as well as with a variety of existing measurements. By using a microscopic quasi-classical Eilenberger equation with the identified triplet pairing function under applied fields, we performed detailed studies of the vortex structures for three phases, including the vortex lattice symmetry, the local density of states, and the internal field distribution. These quantities are directly measurable experimentally by SANS, STM/STS, and NMR, respectively. It is found that, in the B phase of low $H$ and low $T$, the double-core vortex is stabilized over a singular vortex. In the C phase, thermal conductivity data are analyzed to confirm the gap structure proposed. We also give detailed comparisons of various proposed pair functions, concluding that the present scenario of $E_{1u}$ with the $f$-wave, which is an analogue to the triplet planar state, is better than the $E_{2u}$ or $E_{1g}$ scenario. Finally, we discuss the surface topological aspects of Majorana modes associated with the $E_{1u}^f$ state of planar like features.
    Preview · Article · Feb 2012 · Journal of the Physical Society of Japan
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In a promising candidate of topological superconductors, CuxBi2Se3, we propose a way to exclusively determine the pairing symmetry. The proposal suggests that the angle dependence of the thermal conductivity in the basal ab-plane shows a distinct strong anisotropy only when the pairing symmetry is an odd-parity spin-polarized triplet below the superconducting transition temperature (Tc). Such striking isotropy breaking below Tc is explicitly involved in Dirac formalism for superconductors, in which the spin-orbit coupling is essential. We classify possible gap functions based on the Dirac formalism and clarify an origin of the isotropy breaking.
    Preview · Article · Jun 2012 · Physical Review B
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We propose a method utilizing edge current to observe Majorana fermions in the surface Andreev bound state for the superfluid 3He A- and B-phases. The proposal is based on self-consistent analytic solutions of quasi-classical Green's function with an edge. The local density of states and edge mass current in the A-phase or edge spin current in the B-phase can be obtained from these solutions. The edge current carried by the Majorana fermions is partially cancelled by quasiparticles (QPs) in the continuum state outside the superfluid gap. QPs contributing to the edge current in the continuum state are distributed in energy even away from the superfluid gap. The effect of Majorana fermions emerges in the depletion of the edge current by temperature within a low-temperature range. The observations that the reduction in the mass current is changed by T2-power in the A-phase and the reduction in the spin current is changed by T3-power in the B-phase establish the existence of Majorana fermions. We also point out another possibility for observing Majorana fermions by controlling surface roughness.
    Preview · Article · Jul 2012 · Journal of the Physical Society of Japan
Show more