Article

# 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: 7.94). 04/2012; 108(15):157002. DOI: 10.1103/PhysRevLett.108.157002 Source: PubMed

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**ABSTRACT:**Crystal point group symmetry is shown to protect Majorana fermions (MFs) in spinfull superconductors (SCs). We elucidate the condition necessary to obtain MFs protected by the point group symmetry. We reveal that superconductivity in Sr2RuO4 hosts a topological phase transition to a topological crystalline SC, which accompanies a d-vector rotation under a magnetic field along the c-axis. Taking all three bands and spin-orbit interactions into account, symmetry-protected MFs in the topological crystalline SC are identified. Detection of such MFs provides evidence of the d-vector rotation in Sr2RuO4 expected from Knight shift measurements but not yet verified.03/2013; - [Show abstract] [Hide abstract]

**ABSTRACT:**We have investigated the field-angle variation of the specific heat C(H, phi, theta) of the heavy-fermion superconductor UPt3 at low temperatures T down to 50 mK, where phi and theta denote the azimuthal and polar angles of the magnetic field H, respectively. For T = 88 mK, C(H, theta=90) increases proportionally to H^{1/2} up to nearly the upper critical field Hc2, indicating the presence of line nodes. By contrast, C(H, theta=0) deviates upward from the H^{1/2} dependence for (H/Hc2)^{1/2} > 0.5. This behavior can be related to the suppression of Hc2 along the c direction, whose origin has not been resolved yet. Our data show that the unusual Hc2 limit becomes marked only when theta is smaller than 30. In order to explore the possible vertical line nodes in the gap structure, we measured the phi dependence of C in wide T and H ranges. However, we did not observe any in-plane angular oscillation of C within the accuracy of dC/C~0.5%. This result implies that field-induced excitations of the heavy quasiparticles occur isotropically with respect to phi, which is apparently contrary to the recent finding of a twofold thermal-conductivity oscillation.Journal of the Physical Society of Japan 12/2012; 82(2). · 2.09 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**We investigate the topological aspect of the spin-triplet $f$-wave superconductor UPt$_3$ through the microscopic calculations of edge- and vortex-bound states based on the quasiclassical Eilenberger and Bogoliubov-de Gennes theories. It is shown that a gapless and linear dispersion exists at the edge of the $ab$-plane. This forms a Majorana valley, protected by the mirror chiral symmetry. We also demonstrate that with increasing a magnetic field, vortex-bound quasiparticles undergo a topological phase transition from topologically trivial states in the double-core vortex to zero energy states in the normal-core vortex. As long as the ${\bm d}$-vector is locked into the $ab$-plane, the mirror symmetry holds the Majorana property of the zero energy states and thus UPt$_3$ preserves topological crystalline superconductivity robust against the crystal field and spin-orbit interaction.07/2013;

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