Jun Goryo

Multiple superconducting phases in new heavy fermion superconductor PrOs4Sb12

The superconducting gap structure of recently discovered heavy fermion superconductor PrOs4Sb12 was investigated by using thermal transport measurements in magnetic field rotated relative to the crystal axes. We demonstrate that a novel change in the symmetry of the superconducting gap function occurs deep inside the superconducting state, giving a clear indication of the presence of two distinct superconducting phases with twofold and fourfold symmetries. We infer that the gap functions in both phases have a point node singularity, in contrast to the familiar line node singularity observed in almost all unconventional superconductors.

Deconfinement of vortices with continuously variable fractions of the unit flux quanta in two-gap superconductors

We propose a new stage of confinement-deconfinement transition, which can be observed in laboratory. In two-gap superconductors (SCs), two kinds of vortex exist and each of them carries a continuously variable fraction of the unit flux quanta Φ0=hc/2e. The confined state of these two is a usual vortex and stable in the low-temperature region of the system under a certain magnetic field above Hc1. We see an analogy to quarks in a charged pion. An entropy gain causes two fractional vortices to be deconfined above a certain temperature.

Impurity-induced polar Kerr effect in a chiral p-wave superconductor

Recently, the quasi-two-dimensional quasi-2D superconductor Sr2RuO4 with Tc = 1.5 K has attracted considerable attention and it has been investigated extensively. 1 It is plausible that the order parameter in Sr2RuO4 has the spin triplet px ipy-wave symmetry. One of the fascinating properties of this state is the spontaneous breaking of parity in a twodimensional 2D sense px → px and py → �py and in a timereversal symmetry due to the presence of nonzero chirality characterized by lz = 1, where lz is the z component of the relative orbital angular momentum of the Cooper pair. The polar Kerr effect PKE, in which the direction of polarization of reflected linearly polarized light is rotated, has been known as an effective tool for understanding ferromagnetism. 2 Because of the analogy between ferromagnetic order—for instance, with sz = 1 and chiral pair condensation with lz = 1—it is naively expected that the PKE is induced in the chiral p-wave state at zero field. In fact, the PKE has been observed in the superconducting state of Sr2RuO4. 3 Up-to-date theoretical reports on the PKE in the chiral p-wave state are given in Refs. 4 and 5, in which interesting mechanisms have been proposed by the field theoretical approach; however, obtained results of the Kerr rotation angle are considerably smaller than the experimental results. Therefore, it is crucial to elucidate the fundamental nature

Vortex with fractional quantum numbers in a chiralp-wave superconductor

We show that a vortex in a chiral p-wave superconductor, which has the p_{x}+ i p_{y}-wave pairing state and breaks U(1), parity and time reversal symmetry simultaneously, has fractional charge -{n e}/{4} and fractional angular momentum -n^{2}/{16} (n; vorticity). This suggests that the vortex could be anyon and could obey fractional statistics. Electromagnetic property of the vortex is also discussed and we find that an electric field is induced near the vortex core.

Intrinsic Spin Hall Effect in the s-Wave Superconducting State : Analysis of the Rashba Model

A general expression for spin Hall conductivity (SHC) in the s-wave superconducting state at finite temperatures is derived. Based on the expression, we study SHC in a two-dimensional electron gas model in the presence of Rashba spin-orbit interaction (SOI). SHC is zero in the normal state, whereas it takes a large negative value as soon as the superconductivity occurs, due to the change in the quasiparticle contributions. Since this remarkable behavior is independent of the strength of the SOI, it will be widely observed in thin films of superconductors with surface-induced Rashba SOI, or in various noncentrosymmetric superconductors.

Symmetry and Gap Classification of Non-Symmorphic SrPtAs

The hexagonal superconductor SrPtAs exhibits time-reversal symmetry breaking below Tc, hinting at an unconventional pairing state. Therefore, the symmetry of the underlying crystal is important for the classification of possible gap structures and their mixing. Here, we use the generating point group D6h of SrPtAs for a comprehensive classification of the gap functions and to construct a tight-binding model. Our work clarifies questions of symmetry and topology in this non-symmorphic material and allows a better comparison with other hexagonal systems.

The London Equation in Quantum Spin Hall System with Electronic Correlation

The Kane-Mele (KM) model is proposed to describe the quantum spin Hall effect of electrons on the two-dimensional honeycomb lattice. Here, we will show that, in a certain parameter region, the London equation is obtained from the effective field theory of the layered KM model with an electronic correlation.

Quasiparticle Electronic Structure of a New Surperconductor, Y2C3, in the Mixed State Investigated by Specific Heat and Flux-Flow Resistivity

In this paper, we investigate the electronic structure of quasiparticle in the vortex state of Y 2 C 3 by the measurements of the specific heat, C , and the flux-flow resistivity, ρ f . In contrast to a conventional s -wave superconductor, C / T and ρ f showed nonlinear B dependences at low temperatures. The result is discussed in terms of the two gap superconductivity. We estimated the viscosity and the mean free path of the quasiparticles in the vortex core for Y 2 C 3 . While we found that Y 2 C 3 is a clean superconductor in a previous study, the mean free path of the quasiparticles in the vortex core was limited to the coherence length because of the Andreev reflection at the vortex–core boundary in this study.

Flux Flow Resistivity in Two-Gap Superconductor

We investigate the flux flow state in a two-gap superconductor in which two s -wave gaps with different amplitudes exist on two separate Fermi surfaces. The flux flow resistivity is obtained on the...

Vortex pinning in two-gap superconductors

We discuss vortices and their pinning in two-gap superconductors, in which two superconducting gaps are opened around two different Fermi surfaces. We found that there are two kinds of vortices with continuously valuable fractions of the unit flux quanta hc/2e. These two kinds of vortices are tightly bound and cannot be separated in the ground state, but can be when deconfinement occurs by the finite temperature effect as is pointed out (See, Jun Goryo, Shingo Soma, and Hiroshi Matsukawa, Europhys. Lett. 80 (2007) 17002). In this paper, we show that two kinds of vortices can be split by the pinning effect.