920 research outputs found
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
Fulde-Ferrell-Larkin-Ovchinnikov-like state in Ferromagnet-Superconductor Proximity System
We discuss some properties of the ferromagnet-superconductor proximity
system. In particular, the emphasis is put on the physics of the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state. In addition to Andreev
reflections it features a number of unusual thermodynamic and transport
properties, like: oscillatory behavior of the pairing amplitude, density of
states and superconducting transition temperature as a function of the
ferromagnet thickness. Surprisingly, under certain conditions spontaneous spin
polarized current is generated in the ground state of such a system. We provide
some informations regarding experimental observations of this exotic state.Comment: Talk given at Advanced Research Workshop on ''Physics of Spin in
Solids: Materials, Methods & Applications'', Baku (October 2003
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
Gap Nodes and Time Reversal Symmetry Breaking in Strontium Ruthenate
We study the superconducting state of SrRuO on the bases of a
phenomenological but orbital specific description of the electron-electron
attraction and a realistic quantitative account of the electronic structure in
the normal state. We found that a simple model which features both `in plane'
and `out of plane' coupling with strengths meV and
meV respectively reproduced the experimentally observed power law
behaviour of the low temperature specific heat , superfluid density
and thermal conductivity in quantitative detail. Moreover, it predicts
that the quasi-particle spectrum on the -sheet is fully gaped and the
corresponding order parameter breaks the time reversal symmetry. We have also
investigated the stability of this model to inclusion of further interaction
constants in particular %those which describe `proximity coupling' between
orbitals contributing to the sheet of the Fermi surface and the
and sheets. We found that the predictions of the model are
robust under such changes. Finally, we have incorporated a description of weak
disorder into the model and explored some of its consequences. For example we
demonstrated that the disorder has a more significant effect on the -wave
component of the order parameter than on the p-wave one.Comment: EPJ B submitte
Critical current of a Josephson junction containing a conical magnet
We calculate the critical current of a
superconductor/ferromagnetic/superconductor (S/FM/S) Josephson junction in
which the FM layer has a conical magnetic structure composed of an in-plane
rotating antiferromagnetic phase and an out-of-plane ferromagnetic component.
In view of the realistic electronic properties and magnetic structures that can
be formed when conical magnets such as Ho are grown with a polycrystalline
structure in thin-film form by methods such as direct current sputtering and
evaporation, we have modeled this situation in the dirty limit with a large
magnetic coherence length (). This means that the electron mean free
path is much smaller than the normalized spiral length which in
turn is much smaller than (with as the length a complete
spiral makes along the growth direction of the FM). In this physically
reasonable limit we have employed the linearized Usadel equations: we find that
the triplet correlations are short ranged and manifested in the critical
current as a rapid oscillation on the scale of . These rapid
oscillations in the critical current are superimposed on a slower oscillation
which is related to the singlet correlations. Both oscillations decay on the
scale of . We derive an analytical solution and also describe a
computational method for obtaining the critical current as a function of the
conical magnetic layer thickness.Comment: Extended version of the published paper. Additional information about
the computational method is included in the appendi
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