548 research outputs found
Percolation of Superconductivity
In case of superconductors whose electrons attract each other only if they
are near certain centers, the question arises 'How many such centers are needed
to make the ground state superconducting?' We shall examine it in the context
of a random U Hubbard model. In short we study the case where U_i is -|U| and 0
with probability c and 1-c respectively on a lattice whose sites are labelled i
using the Gorkov decoupling and the Coherent Potential Approximation (CPA). We
argue that for this model there is a critical concentration c_0 below which the
system is not a superconductor.Comment: 18 pages, 10 figure
Spontaneous currents in a ferromagnet - normal metal - superconductor trilayer
We discuss the ground state properties of the system composed of a normal
metal sandwiched between ferromagnet and superconductor within a tight binding
Hubbard model. We have solved the spin-polarized Hartree-Fock-Gorkov equations
together with the Maxwell's equation (Ampere's law) and found a proximity
induced Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in this system. Here we
show that the inclusion of the normal metal layer in between those subsystems
does not necessarily lead to the suppression of the FFLO phase. Moreover, we
have found that depending on the thickness of the normal metal slab the system
can be switched periodically between the state with the spontaneous current
flowing to that one with no current. All these effects can be explained in
terms of the Andreev bound states formed in such structures.Comment: 6 pages, 4 figure
Spin Polarized Current in the Ground State of Superconductor - Ferromagnet - Insulator Trilayers
We study the ground state properties of a superconductor - ferromagnet -
insulator trilayer on the basis of a Hubbard Model featuring exchange splitting
in the ferromagnet and electron - electron attraction in the superconductor. We
solve the spin - polarized Hartree - Fock - Gorkov equations together with the
Maxwell's equation (Ampere's law) fully self-consistently. For certain values
of the exchange splitting we find that a spontaneous spin polarized current is
generated in the ground state and is intimately related to Andreev bound states
at the Fermi level. Moreover, the polarization of the current strongly depends
on the band filling.Comment: 13 pages, 14 figure
Optical properties of random alloys : Application to Cu_{50}Au_{50} and Ni_{50}Pt_{50}
In an earlier paper [K. K. Saha and A. Mookerjee, Phys. Rev. B 70 (2004) (in
press) or, cond-mat/0403456] we had presented a formulation for the calculation
of the configuration-averaged optical conductivity in random alloys. Our
formulation is based on the augmented-space theorem introduced by one of us [A.
Mookerjee, J. Phys. C: Solid State Phys. 6, 1340 (1973)]. In this communication
we shall combine our formulation with the tight-binding linear muffin-tin
orbitals (TB-LMTO) technique to study the optical conductivities of two alloys
Cu_{50}Au_{50} and Ni_{50}Pt_{50}.Comment: 5 pages, 7 figure
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