1,619 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
The electronic Hamiltonian for cuprates
A realistic many-body Hamiltonian for the cuprate superconductors should include both copper d and oxygen p states, hopping matrix elements between them, and Coulomb energies, both on-site and inter-site. We have developed a novel computational scheme for deriving the relevant parameters ab initio from a constrained occupation local density functional. The scheme includes numerical calculation of appropriate Wannier functions for the copper and oxygen states. Explicit parameter values are given for La2CuO4. These parameters are generally consistent with other estimates and with the observed superexchange energy. Secondly, we address whether this complicated multi-band Hamiltonian can be reduced to a simpler one with fewer basis states per unit cell. We propose a mapping onto a new two-band effective Hamiltonian with one copper d and one oxygen p derived state per unit cell. This mapping takes into account the large oxygen-oxygen hopping given by the ab initio calculations
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
Tilt Grain-Boundary Effects in S- and D-Wave Superconductors
We calculate the s- and d-wave superconductor order parameter in the vicinity
of a tilt grain boundary. We do this self-consistently within the Bogoliubov de
Gennes equations, using a realistic microscopic model of the grain boundary. We
present the first self-consistent calculations of supercurrent flows in such
boundaries, obtaining the current-phase characteristics of grain boundaries in
both s-wave and d-wave superconductors
Physical Mechanism of the d->d+is Transition
We discuss the basic physical mechanism of the d->d+is transition, which is
the currently accepted explanation for the results of tunneling experiments
into planes. Using the first-order perturbation theory, we show that the
zero-bias states drive the transition. We present various order-of-magnitude
estimates and consistency checks that support this picture.Comment: 7 pages, 2 figure
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