2,194 research outputs found
Quantum Corrals, Eigenmodes and Quantum Mirages in s-wave Superconductors
We study the electronic structure of magnetic and non-magnetic quantum
corrals embedded in s-wave superconductors. We demonstrate that a quantum
mirage of an impurity bound state peak can be projected from the occupied into
the empty focus of a non-magnetic quantum corral via the excitation of the
corral's eigenmodes. We observe an enhanced coupling between magnetic
impurities inside the corral, which can be varied through oscillations in the
corral's impurity potential. Finally, we discuss the form of eigenmodes in
magnetic quantum corrals.Comment: 4 pages, 4 figure
Theoretical study of a localized quantum spin reversal by the sequential injection of spins in a spin quantum dot
This is a theoretical study of the reversal of a localized quantum spin
induced by sequential injection of spins for a spin quantum dot that has a
quantum spin. The system consists of ``electrode/quantum
well(QW)/dot/QW/electrode" junctions, in which the left QW has an energy level
of conduction electrons with only up-spin. We consider a situation in which
up-spin electrons are sequentially injected from the left electrode into the
dot through the QW and an exchange interaction acts between the electrons and
the localized spin. To describe the sequentially injected electrons, we propose
a simple method based on approximate solutions from the time-dependent
Schrdinger equation. Using this method, it is shown that the spin
reversal occurs when the right QW has energy levels of conduction electrons
with only down-spin. In particular, the expression of the reversal time of a
localized spin is derived and the upper and lower limits of the time are
clearly expressed. This expression is expected to be useful for a rough
estimation of the minimum relaxation time of the localized spin to achieve the
reversal. We also obtain analytic expressions for the expectation value of the
localized spin and the electrical current as a function of time. In addition,
we found that a system with the non-magnetic right QW exhibits spin reversal or
non-reversal depending on the exchange interaction.Comment: 12 pages, 12 figures, to be published in Phys. Rev. B, typos
correcte
spl(2,1) dynamical supersymmetry and suppression of ferromagnetism in flat band double-exchange models
The low energy spectrum of the ferromagnetic Kondo lattice model on a N-site
complete graph extended with on-site repulsion is obtained from the underlying
spl(2,1) algebra properties in the strong coupling limit. The ferromagnetic
ground state is realized for 1 and N+1 electrons only. We identify the large
density of states to be responsible for the suppression of the ferromagnetic
state and argue that a similar situation is encountered in the Kagome,
pyrochlore, and other lattices with flat bands in their one-particle density of
states.Comment: 7 pages, 1 figur
Spin dynamics of a one-dimensional spin-1/2 fully anisotropic Ising-like antiferromagnet in a transverse magnetic field
We consider the one-dimensional Ising-like fully anisotropic S=1/2 Heisenberg
antiferromagnetic Hamiltonian and study the dynamics of domain wall excitations
in the presence of transverse magnetic field . We obtain dynamical spin
correlation functions along the magnetic field and
perpendicular to it . It is shown that the line shapes of
and are purely symmetric at the
zone-boundary. It is observed in for that the
spectral weight moves toward low energy side with the increase of . This
model is applicable to study the spin dynamics of CsCoCl in the presence of
weak interchain interactions.Comment: 19 pages, LaTeX, 12 eps figure
Susceptibility of the one-dimensional, dimerized Hubbard model
We show that the zero temperature susceptibility of the one-dimensional,
dimerized Hubbard model at quarter-filling can be accurately determined on the
basis of exact diagonalization of small clusters. The best procedure is to
perform a finite-size scaling of the spin velocity , and to calculate
the susceptibility from the Luttinger liquid relation . We
show that these results are reliable by comparing them with the analytical
results that can be obtained in the weak and strong coupling limits. We have
also used quantum Monte Carlo simulations to calculate the temperature
dependence of the susceptibility for parameters that should be relevant to the
Bechgaard salts. This shows that, used together, these numerical techniques are
able to give precise estimates of the low temperature susceptibility of
realistic one-dimensional models of correlated electrons.Comment: 10 pages, latex, figures available from the authors. To appear in
Phys. Rev. B, Rapid Comm
Immobilization of a carbon nanomaterial-based localized drug-release system using a bispecific material-binding peptide
Phase Diagram of Lattice-Spin System RbCoBr
We study the lattice-spin model of RbCoBr which is proposed by Shirahata
and Nakamura, by mean field approximation. This model is an Ising spin system
on a distorted triangular lattice. There are two kinds of frustrated variables,
that is, the lattice and spin. We obtain a phase diagram of which phase
boundary is drawn continuously in a whole region. Intermediate phases that
include a partial disordered state appear. The model has the first-order phase
transitions in addition to the second-order phase transitions. We find a
three-sublattice ferrimagnetic state in the phase diagram. The three-sublattice
ferrimagnetic state does not appear when the lattice is not distorted.Comment: 5 pages, 4 figures, jpsj2.cls, to be published in J. Phys. Soc. Jpn.
Vol.75 (2006) No.
Pairbreaking Without Magnetic Impurities in Disordered Superconductors
We study analytically the effects of inhomogeneous pairing interactions in
short coherence length superconductors, using a spatially varying
Bogoliubov-deGennes model. Within the Born approximation, it reproduces all of
the standard Abrikosov-Gor'kov pairbreaking and gaplessness effects, even in
the absence of actual magnetic impurities. For pairing disorder on a single
site, the T-matrix gives rise to bound states within the
BCS gap. Our results are compared with recent scanning tunneling microscopy
measurements on BiSrCaCuO with Zn or Ni impurities.Comment: 4 pages, 2 figures, submitted to PR
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