arXiv subjects

Michał Zegrodnik

Publications and source records attributed to Michał Zegrodnik.

22 records · Page 2Linked to original sources

arXiv2015

Fulde-Ferrell state induced purely by the orbital effect in a superconducting nanowire

We demonstrate that the Fulde-Ferrell (FF) phase can be induced uniquely by the orbital effect in a cylindrical metallic nanowire. In the external magnetic field the two-fold degeneracy with respect to the orbital quantum number $m$ is lifted what leads to a Fermi wave vector mismatch between the subbands with opposite orbital momenta in the paired state. This mismatch can be compensated by the nonzero total momentum of the Cooper pairs created by electrons from split subbands what results in the formation of the FF phase. With increasing magnetic field a series of FF stability regions appear in between which the standard BCS superconducting phase is stable.

cond-mat.supr-con↗

arXiv2014

Spontaneous appearance of nonzero momentum Cooper pairing: Possible application to the iron-pnictides

We suggest that an inhomogeneous (non-zero momentum) paired phase can appear in the absence of an external magnetic field in the system with a predominant interband pairing and with separate Fermi-surface sheets. The Fermi wave vector mismatch which appears in such situation can be compensated by nonzero center-of-mass momentum of the Cooper pairs, what can lead to a spontaneous appearance of the Fulde-Ferrell type of superconducting state. The idea is examined using a tight-binding model which emulates the hole-like and the electron-like bands of iron based superconductor. The state can appear for the case of both spin-singlet and -triplet pairing channels.

cond-mat.supr-con↗

arXiv2013

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.

cond-mat.supr-con↗

arXiv2013

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.

cond-mat.supr-con↗