Realization of Berezinskii's superconductivity in quasi-one-dimensional systems

We revisit the pairing symmetry competition in quasi-one-dimensional systems. We show that spin-triplet s-wave pairing, where the pair is formed by electrons with different times and has an odd-frequency symmetry, can be realized in systems with strong one-dimensionality when the strength of charge fluctuation dominates over spin fluctuation. The present study provides a novel microscopic mechanism for this exotic pairing originally proposed by Berezinskii in 1974.Comment: 4 pages, 4 figure

Dynamical Generation of Non-Abelian Gauge Group via the Improved Perturbation Theory

It was suggested that the massive Yang-Mills-Chern-Simons matrix model has three phases and that in one of them a non-Abelian gauge symmetry is dynamically generated. The analysis was at the one-loop level around a classical solution of fuzzy sphere type. We obtain evidences that three phases are indeed realized as nonperturbative vacua by using the improved perturbation theory. It also gives a good example that even if we start from a trivial vacuum, the improved perturbation theory around it enables us to observe nontrivial vacua.Comment: 31 pages, published versio

A unified origin for the 3D magnetism and superconductivity in Nax_xCoO2_2

We analyze the origin of the three dimensional (3D) magnetism observed in nonhydrated Na-rich Na$_x$CoO$_2$ within an itinerant spin picture using a 3D Hubbard model. The origin is identified as the 3D nesting between the inner and outer portions of the Fermi surface, which arise due to the local minimum structure of the $a_{1g}$ band at the $\Gamma$-A line. The calculated spin wave dispersion strikingly resembles the neutron scattering result. We argue that this 3D magnetism and the spin fluctuations responsible for superconductivity in the hydrated systems share essentially the same origin.Comment: 5pages, 6figure

Hole Pairs in the Two-Dimensional Hubbard Model

The interactions between holes in the Hubbard model, in the low density, intermediate to strong coupling limit, are investigated. Dressed spin polarons in neighboring sites have an increased kinetic energy and an enhanced hopping rate. Both effects are of the order of the hopping integral and lead to an effective attraction at intermediate couplings. Our results are derived by systematically improving mean field calculations. The method can also be used to derive known properties of isolated spin polarons.Comment: 4 page

Superconducting Fluctuations in a Multi-Band 1D Hubbard Model

A renormalization-group and bosonization approach for a multi-band Hubbard Hamiltonian in one dimension is described. Based on the limit of many bands, it is argued that this Hamiltonian with bare repulsive electron-electron interactions is scaled under specific conditions to a model in which superconducting fluctuations dominate.Comment: 12 pages + 1 fig, Revtex, Preprint - Los Alamo

Spin-fluctuation exchange study of superconductivity in two- and three-dimensional single-band Hubbard models

In order to identify the most favorable situation for superconductivity in the repulsive single-band Hubbard model, we have studied instabilities for d-wave pairing mediated by antiferromagnetic spin fluctuations and p-pairing mediated by ferromagnetic fluctuations with the fluctuation exchange approximation in both two dimensions and three dimensions. By systematically varying the band filling and band structure we have shown that (i) d-pairing is stronger in two dimensions than in three dimensions, and (ii) p-pairing is much weaker than the d-pairing.Comment: RevTex, 5 figures in Postscript, to be published in Phys. Rev.

Renormalization Group Technique Applied to the Pairing Interaction of the Quasi-One-Dimensional Superconductivity

A mechanism of the quasi-one-dimensional (q1d) superconductivity is investigated by applying the renormalization group techniques to the pairing interaction. With the obtained renormalized pairing interaction, the transition temperature Tc and corresponding gap function are calculated by solving the linearized gap equation. For reasonable sets of parameters, Tc of p-wave triplet pairing is higher than that of d-wave singlet pairing due to the one-dimensionality of interaction. These results can qualitatively explain the superconducting properties of q1d organic conductor (TMTSF)2PF6 and the ladder compound Sr2Ca12Cu24O41.Comment: 18 pages, 9 figures, submitted to J. Phys. Soc. Jp