74,477 research outputs found
Theory of the proximity effect in junctions with unconventional superconductors
We present a general theory of the proximity effect in junctions between
diffusive normal metals (DN) and unconventional superconductors in the
framework of the quasiclassical Green's function formalism. Various possible
symmetry classes in a superconductor are considered which are consistent with
the Pauli principle: even-frequency spin-singlet even-parity (ESE) state,
even-frequency spin-triplet odd-parity (ETO) state, odd-frequency spin-triplet
even-parity (OTE) state and odd-frequency spin-singlet odd-parity (OSO) state.
For each of the above four cases symmetry and spectral properties of the
induced pair amplitude in the DN are determined. It is shown that the pair
amplitude in a DN belongs respectively to an ESE, OTE, OTE and ESE pairing
state.Comment: 5 pages with one figur
Stability of ferromagnetism in the Hubbard model on the kagom\'e lattice
The Hubbard model on the kagom\'e lattice has highly degenerate ground states
(the flat lowest band) in the corresponding single-electron problem and
exhibits the so-called flat-band ferromagnetism in the many-electron ground
states as was found by Mielke. Here we study the model obtained by adding extra
hopping terms to the above model. The lowest single-electron band becomes
dispersive, and there is no band gap between the lowest band and the other
band. We prove that, at half-filling of the lowest band, the ground states of
this perturbed model remain saturated ferromagnetic if the lowest band is
nearly flat.Comment: 4 pages, 1 figur
Optimal Output Feedback Architecture for Triangular LQG Problems
Distributed control problems under some specific information constraints can
be formulated as (possibly infinite dimensional) convex optimization problems.
The underlying motivation of this work is to develop an understanding of the
optimal decision making architecture for such problems. In this paper, we
particularly focus on the N-player triangular LQG problems and show that the
optimal output feedback controllers have attractive state space realizations.
The optimal controller can be synthesized using a set of stabilizing solutions
to 2N linearly coupled algebraic Riccati equations, which turn out to be easily
solvable under reasonable assumptions.Comment: To be presented at 2014 American Control Conferenc
Buckling of swelling gels
The patterns arising from the differential swelling of gels are investigated
experimentally and theoretically as a model for the differential growth of
living tissues. Two geometries are considered: a thin strip of soft gel clamped
to a stiff gel, and a thin corona of soft gel clamped to a disk of stiff gel.
When the structure is immersed in water, the soft gel swells and bends out of
plane leading to a wavy periodic pattern which wavelength is measured. The
linear stability of the flat state is studied in the framework of linear
elasticity using the equations for thin plates. The flat state is shown to
become unstable to oscillations above a critical swelling rate and the computed
wavelengths are in quantitative agreement with the experiment
Uniaxial pressure dependencies of the phase boundary of TlCuCl_3
We present a thermal expansion and magnetostriction study of TlCuCl_3, which
shows a magnetic-field induced transition from a spin gap phase to a Neel
ordered phase. Using Ehrenfest relations we derive huge and strongly
anisotropic uniaxial pressure dependencies of the respective phase boundary,
e.g. the transition field changes by about GPa depending on the
direction of uniaxial pressure.Comment: 2 pages, e figures; presented at SCES200
Theory of proximity effect in ferromagnet/superconductor heterostructures in the presence of spin dependent interfacial phase shift
We study the proximity effect and charge transport in ferromagnet (F)/superconductor (S) and S/F/I/F/S junctions (where I is insulator) by taking into account simultaneously exchange field in F and spin-dependent interfacial phase shifts (SDIPS) at the F/S interface. We solve the Usadel equations using extended Kupriyanov–Lukichev boundary conditions which include SDIPS, where spin-independent part of tunneling conductance GT and spin-dependent one Gφ coexist. The resulting local density of states (LDOS) in a ferromagnet depends both on the exchange energy Eex and Gφ/GT. We show that the magnitude of zero-temperature gap and the height of zero-energy LDOS have a non-monotonic dependence on Gφ/GT. We also calculate Josephson current in S/F/I/F/S junctions and show that crossover from 0-state to
Diffractive heavy pseudoscalar-meson productions by weak neutral currents
A first theoretical study for neutrino-induced diffractive productions of
heavy pseudoscalar-mesons, \eta_c and \eta_b, off a nucleon is performed based
on factorization formalism in QCD. We evaluate the forward diffractive
production cross section in perturbative QCD in terms of the light-cone wave
functions of Z boson and \eta_{c,b} mesons, and the gluon distribution of the
nucleon. The diffractive production of \eta_c is governed by the axial vector
coupling of the longitudinally polarized Z boson to Q\bar{Q} pair, and the
resulting \eta_c production cross section is larger than the J/\psi one by one
order of magnitude. The bottomonium \eta_b production, which shows up for
higher beam energy, is also discussed.Comment: 5 pages with 3 embedded figures. Talk presented at the 15th
International Spin Physics Symposium, Spin 2002, Brookhaven National
Laboratory, September 9-14, 200
Anomalous Josephson effect in d-wave superconductor junctions on TI surface
We study Josephson effect of -wave superconductor (DS)/ferromagnet
insulator(FI)/DS junctions on a surface of topological insulator (TI). We
calculate Josephson current for various orientations
of the junctions where is the macroscopic phase difference between
two DSs. In certain configurations, we find anomalous current-phase relation
with periodicity. In the
case where the first order Josephson coupling is absent without magnetization
in FI, can be proportional to . The magnitude of the
obtained Josephson current is enhanced due to the zero energy states on the
edge of DS on TI. Even if we introduce an -wave component of pair potential
in DS, we can still expect the anomalous current-phase relation in asymmetric
DS junctions with . This can be used to probe
the induced -wave component of pair potential on TI surface in high-
cuperate/TI hybrid structures.Comment: 6 pages, 4 figure
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