Yoshiki Imai

Properties of edge states in a spin-triplet two-band superconductor

Motivated by Sr2RuO4 the magnetic properties of edge states in a two-band spin-triplet superconductor with electron- and hole-like Fermi surfaces are investigated assuming chiral p-wave pairing symmetry. The two bands correspond to the alpha-beta-bands of Sr2RuO4 and are modeled within a tight-binding model including inter-orbital hybridization and spin-orbit coupling effects. Including superconductivity the quasiparticle spectrum is determined by means of a self-consistent Bogolyubov-de Gennes calculation. While a full quasiparticle excitation gap appears in the bulk, gapless states form at the edges which produce spontaneous spin and/or charge currents. The spin current is the result of the specific band structure while the charge current originates from the superconducting condensate. Together they induce a small spin polarization at the edge. Furthermore onsite Coulomb repulsion is included to show that the edge states are unstable against the formation of a Stoner-like spin polarization of the edge states. Through spin-orbit coupling the current- and the correlation-induced magnetism are coupled to the orientation of the chirality of the superconducting condensate. We speculate that this type of phenomenon could yield a compensation of the magnetic fields induced by currents and also explain the negative result in the recent experimental search for chiral edge currents.

Anomalous Metal–Insulator Transition in Filled Skutterudite CeOs4Sb12

Anomalous metal–insulator transition observed in filled skutterudite CeOs 4 Sb 12 is investigated by constructing the effective tight-binding model with the Coulomb repulsion between f electrons. B...

Topological and edge state properties of a three-band model for Sr2RuO4

Modeling the spin-triplet superconductor Sr2RuO4 through a three-orbital tight-binding model we investigate topological properties and edge states assuming chiral p-wave pairing. In concordance with experiments the three Fermi surfaces consist of two electron-like and one hole-like one corresponding to the alpha-, beta- and gamma-band on the level of a two-dimensional system. The quasi-particle spectra and other physical quantities of the superconducting phase are calculated by means of a self-consistent Bogoliubov-de Gennes approach for a ribbon shaped system. While a full quasiparticle excitation gap is realized in the bulk system, at the edges gapless states appear some of which have linear and others nearly flat dispersion around zero energy. This study shows the interplay between spin-orbit coupling induced spin currents, chiral edge currents and correlation driven surface magnetism. The topological nature of the chiral p-wave state manifests itself in the gamma-band characterized by an integer Chern number. As the gamma-band is close to a Lifshitz transition in Sr2RuO4, changing the sign of the Chern number, the topological nature may be rather fragile.

Absence of Hybridization Gap in Heavy Electron Systems and Analysis of YbAl3 in Terms of Nearly Free Electron Conduction Band

In the analysis of the heavy electron systems, theoretical models with c–f hybridization gap are often used. We point out that such a gap does not exist and the simple picture with the hybridizatio...

Thermal Hall conductivity and topological transition in a chiral p-wave superconductor for Sr2RuO4

The interplay between the thermal transport property and the topological aspect is investigated in a spin-triplet chiral p-wave superconductor Sr2RuO4 with the strong two-dimensionality. We show the thermal Hall conductivity is well described by the temperature linear term and the exponential term in the low temperature region. While the former term is proportional to the so-called Chern number directly, the latter is associated with the superconducting gap amplitude of the gamma band. We also demonstrate that the coefficient of the exponential term changes the sign around Lifshitz transition. Our obtained result may enable us access easily the physical quantities and the topological property of Sr2RuO4 in detail.

Applications of path-integral renormalization group method combined with density functional theory.

The path-integral renormalization group method is an efficient tool for computing electronic structure of strongly correlated electron systems. Combined with the conventional density functional approaches as a hybrid scheme, it offers a first-principles method for complex materials with involved electron correlation effects. We assess the efficiency and applicability of the hybrid scheme by examining applications to Sr(2)VO(4) and YVO(3).

Surface magnetism in a chiral d-wave superconductor with hexagonal symmetry

Surface properties are examined in a chiral d-wave superconductor with hexagonal symmetry, whose one-body Hamiltonian possesses the intrinsic spin-orbit coupling identical to the one characterizing the topological nature of the Kane-Mele honeycomb insulator. In the normal state spin-orbit coupling gives rise to spontaneous surface spin currents, whereas in the superconducting state there exist besides the spin currents also charge surface currents, due to the chiral pairing symmetry. Interestingly, the combination of these two currents results in a surface spin polarization, whose spatial dependence is markedly different on the zigzag and armchair surfaces. We discuss various potential candidate materials, such as SrPtAs, which may exhibit these surface properties.

Anomalous magnetic phase diagram in low-carrier two-band systems and possible application to Ce Os 4 Sb 12

Magnetic properties under the external field are investigated in low-carrier two-band systems, which may explain the nontrivial phase boundary found in temperature vs magnetic field diagram discovered in some materials, such as filled-skutterudite compound

Effect of the RuO6 Octahedron Rotation at the Sr2RuO4 Surface on Topological Property

\mathrm{Ce}{\mathrm{Os}}_{4}{\mathrm{Sb}}_{12}

Theory for magnetic anisotropy of field-induced insulator-to-metal transition in cubic kondo insulator YbB12

. Analysis is made both for the periodic Anderson model with the small-dispersive