1,054 research outputs found
On the scaling approach to electron-electron interactions in a chaotic quantum dot
A scaling theory is used to study the low energy physics of electron-electron
interactions in a double quantum dot. We show that the fact that electrons are
delocalized over two quantum dots does not affect the instability criterion for
the description of electron-electron interactions in terms of a ``universal
interaction Hamiltonian''.Comment: 4 pages, 3 figure
Role of a parallel magnetic field in two dimensional disordered clusters containing a few correlated electrons
An ensemble of 2d disordered clusters with a few electrons is studied as a
function of the Coulomb energy to kinetic energy ratio r_s. Between the Fermi
system (small r_s) and the Wigner molecule (large r_s), an interaction induced
delocalization of the ground state takes place which is suppressed when the
spins are aligned by a parallel magnetic field. Our results confirm the
existence of an intermediate regime where the Wigner antiferromagnetism
defavors the Stoner ferromagnetism and where the enhancement of the Lande g
factor observed in dilute electron systems is reproduced.Comment: 4 pages, 3 figure
Spin and Charge Correlations in Quantum Dots: An Exact Solution
The inclusion of charging and spin-exchange interactions within the Universal
Hamiltonian description of quantum dots is challenging as it leads to a
non-Abelian action. Here we present an {\it exact} analytical solution of the
probem, in particular, in the vicinity of the Stoner instabilty point. We
calculate several observables, including the tunneling density of states (TDOS)
and the spin susceptibility. Near the instability point the TDOS exhibits a
non-monotonous behavior as function of the tunneling energy, even at
temperatures higher than the exchange energy. Our approach is generalizable to
a broad set of observables, including the a.c. susceptibility and the
absorption spectrum for anisotropic spin interaction. Our results could be
tested in nearly ferromagnetic materials.Comment: JETPL class, 6 pages, 2 figure
Spin and interaction effects in quantum dots: a Hartree-Fock-Koopmans approach
We use a Hartree-Fock-Koopmans approach to study spin and interaction effects
in a diffusive or chaotic quantum dot. In particular, we derive the statistics
of the spacings between successive Coulomb-blockade peaks. We include
fluctuations of the matrix elements of the two-body screened interaction,
surface-charge potential, and confining potential to leading order in the
inverse Thouless conductance. The calculated peak-spacing distribution is
compared with experimental results.Comment: 5 pages, 4 eps figures, revise
An efficient Fredholm method for calculation of highly excited states of billiards
A numerically efficient Fredholm formulation of the billiard problem is
presented. The standard solution in the framework of the boundary integral
method in terms of a search for roots of a secular determinant is reviewed
first. We next reformulate the singularity condition in terms of a flow in the
space of an auxiliary one-parameter family of eigenproblems and argue that the
eigenvalues and eigenfunctions are analytic functions within a certain domain.
Based on this analytic behavior we present a numerical algorithm to compute a
range of billiard eigenvalues and associated eigenvectors by only two
diagonalizations.Comment: 15 pages, 10 figures; included systematic study of accuracy with 2
new figures, movie to Fig. 4,
http://www.quantumchaos.de/Media/0703030media.av
Gossip in the workplace and the implications for HR management : a study of gossip and its relationship to employee cynicism
Gossip is a common phenomenon in the workplace and yet relatively little is understood about its
influence to employees. This study adopts social information theory and social cognitive theory to interpret
the diverse literature on gossip, and to develop and test hypotheses concerning some of the antecedents of
gossip, with an aim of developing knowledge of the relationship between gossip and employee behaviour in
the workplace. The study analysed survey data in a two stage process, from 362 employees across a range
of industries in Taiwan. The findings revealed that job-related gossip predicted employee cynicism and
mediated the relationship between psychological contract violation and cynicism, and that non-job-related
gossip showed a similar but weaker effect to employee cynicism. The contribution made by this paper is of
value to both the academic subject domain and managers in Human Resources. Firstly, we have identified
two constructs of gossip, job related and non-job related gossip not previously reported and a validated scale
has been created. Secondly, we have confirmed that these different constructs of gossip impact differently on
employee behaviour and therefore HR managers should be cautious about gossip in the workplace, as it can
cause cynical behaviour amongst employees
Linear conductance in Coulomb-blockade quantum dots in the presence of interactions and spin
We discuss the calculation of the linear conductance through a
Coulomb-blockade quantum dot in the presence of interactions beyond the
charging energy. In the limit where the temperature is large compared with a
typical tunneling width, we use a rate-equations approach to describe the
transitions between the corresponding many-body states. We discuss both the
elastic and rapid-thermalization limits, where the rate of inelastic scattering
in the dot is either small or large compared with the elastic transition rate,
respectively. In the elastic limit, we find several cases where a closed
solution for the conductance is possible, including the case of a constant
exchange interaction. In the rapid-thermalization limit, a closed solution is
possible in the general case. We show that the corresponding expressions for
the linear conductance simplify for a Hamiltonian that is invariant under spin
rotations.Comment: 11 pages, no figures, revtex
Mesoscopic interplay of superconductivity and ferromagnetism in ultra-small metallic grains
We review the effects of electron-electron interactions on the ground-state
spin and the transport properties of ultra-small chaotic metallic grains. Our
studies are based on an effective Hamiltonian that combines a superconducting
BCS-like term and a ferromagnetic Stoner-like term. Such terms originate in
pairing and spin exchange correlations, respectively. This description is valid
in the limit of a large dimensionless Thouless conductance. We present the
ground-state phase diagram in the fluctuation-dominated regime where the
single-particle mean level spacing is comparable to the bulk BCS pairing gap.
This phase diagram contains a regime in which pairing and spin exchange
correlations coexist in the ground-state wave function. We discuss the
calculation of the tunneling conductance for an almost-isolated grain in the
Coulomb-blockade regime, and present measurable signatures of the competition
between superconductivity and ferromagnetism in the mesoscopic fluctuations of
the conductance.Comment: 6 pages, 3 figures, To be published in the proceedings of the NATO
Advance Research Workshop "Recent Advances in Nonlinear Dynamics and Complex
System Physics.
Kondo effect in real quantum dots
Exchange interaction within a quantum dot strongly affects the transport
through it in the Kondo regime. In a striking difference with the results of
the conventional model, where this interaction is neglected, here the
temperature and magnetic field dependence of the conductance may become
non-monotonic: its initial increase follows by a drop when temperature and
magnetic field are lowered
Mesoscopic Tunneling Magnetoresistance
We study spin-dependent transport through
ferromagnet/normal-metal/ferromagnet double tunnel junctions in the mesoscopic
Coulomb blockade regime. A general transport equation allows us to calculate
the conductance in the absence or presence of spin-orbit interaction and for
arbitrary orientation of the lead magnetizations. The tunneling
magnetoresistance (TMR), defined at the Coulomb blockade conductance peaks, is
calculated and its probability distribution presented. We show that mesoscopic
fluctuations can lead to the optimal value of the TMR.Comment: 5 pages, 3 eps figures included using epsf.sty. Revised text and
improved notation, fig. 2 removed, explicit equations for the GSE case adde
- …