Seebeck effect in the graphene-superconductor junction

Thermopower of graphene-superconductor (GS) junction is analyzed within the extended Blonder- Tinkham-Klapwijk formalism. Within this approach we have also calculated the temperature de- pendence of the zero-bias conductance for GS junction. Both quantities reflect quasi-relativistic nature of massless Dirac fermions in graphene. Both, the linear and the non-linear regimes are considered.Comment: 5 pages, 4 figure

Coexistence of spin-triplet superconductivity with magnetic ordering in an orbitally degenerate system: Hartree-Fock-BCS approximation revisited

The Hund's-rule-exchange induced and coexisting spin-triplet paired and magnetic states are considered within the doubly degenerate Hubbard model with interband hybridization. The Hartree-Fock approximation combined with the Bardeen-Cooper-Schrieffer (BCS) approach is analyzed for the case of square lattice. The calculated phase diagram contains regions of stability of the spin-triplet superconducting phase coexisting with either ferromagnetism or antiferromagnetism, as well as a pure superconducting phase. The influence of the inter-site hybridization on the stability of the considered phases, as well as the temperature dependence of both the magnetic moment and the superconducting gaps, are also discussed. Our approach supplements the well known phase diagrams containing only magnetic phases with the paired triplet states treated on the same footing. We also discuss briefly how to include the spin fluctuations within this model with real space pairing

Universal scaling and quantum critical behavior of CeRhSb(1-x)Sn(x)

We propose a universal scaling rho*chi=const of the electrical resistivity rho with the inverse magnetic susceptibility chi^(-1) below the temperature of the quantum-coherence onset for the Ce 4f states in CeRhSb(1-x)Sn(x). In the regime, where the Kondo gap disappears (x~0.12), the system forms a non-Fermi liquid (NFL), which transforms into a Fermi liquid at higher temperature. The NFL behavior is attributed to the presence of a novel quantum critical point (QCP) at the Kondo insulator - correlated metal boundary. The divergent behavior of the resistivity, the susceptibility, and the specific heat has been determined when approaching QCP from the metallic side.Comment: Sent to Phys. Rev. Let

Lieb-Wu Solution, Gutzwiller-Wave-Function, and Gutzwiller-Ansatz Approximation, with Adjustable Single-Particle Wave Function for the Hubbard Chain

The optimized single-particle wave functions contained in the parameters of the Hubbard model (t and U) were determined for an infinite atomic chain. In effect, the electronic properties of the chain as a function of interatomic distance R were obtained and compared for the Lieb - Wu exact solution (LW), the Gutzwiller-Wave-Function approximation (GWF), and the Gutzwiller-ansatz case (GA). The ground state energy and other characteristics for the infinite chain were also compared with those obtained earlier for a nanoscopic chain within the Exact Diagonalization combined with an Ab Initio adjustment of the single-particle wave functions in the correlated state (EDABI method). For the sake of completeness, we briefly characterize also each of the solutions. Our approach completes the Lieb-Wu solution, as it provides the system electronic properties evolution as a function of physically controllable parameter - the interatomic distance.Comment: 17 pages, 8 figures, 2 table

Even-parity spin-triplet pairing for orbitally degenerate correlated electrons by purely repulsive interactions

We demonstrate the stability of a spin-triplet paired s-wave (with an admixture of extended s-wave) state for the case of purely repulsive interactions in a degenerate two-band Hubbard model. We further show that near half-filling the considered kind of superconductivity can coexist with antiferromagnetism. The calculations have been carried out with the use of the so-called statistically consistent Gutzwiller approximation for the case of a square lattice. The absence of a stable paired state when analyzed in the Hartree-Fock-BCS approximation allows us to claim that the electron correlations in conjunction with the Hund's rule exchange play the crucial role in stabilizing the spin-triplet superconducting state. A sizable hybridization of the bands suppresses the paired state

Conductance of a double quantum dot with correlation-induced wave function renormalization

The zero-temperature conductance of diatomic molecule, modelled as a correlated double quantum dot attached to noninteracting leads is investigated. We utilize the Rejec-Ramsak formulas, relating the linear-response conductance to the ground-state energy dependence on magnetic flux within the framework of EDABI method, which combines exact diagonalization with ab initio calculations. The single-particle basis renormalization leads to a strong particle-hole asymmetry, of the conductance spectrum, absent in a standard parametrized model study. We also show, that the coupling to leads V=0.5t (t is the hopping integral) may provide the possibility for interatomic distance manipulation due to the molecule instability.Comment: Presented on the The International Conference on Strongly Correlated Electron Systems SCES'05, July 26-30th 2005, Vienna, Austria. An abbreviated version will appear in Physica