49 research outputs found
Implementation of transmission functions for an optimized three-terminal quantum dot heat engine
We consider two modifications of a recently proposed three-terminal quantum
dot heat engine. First, we investigate the necessity of the thermalization
assumption, namely that electrons are always thermalized by inelastic processes
when traveling across the cavity where the heat is supplied. Second, we analyze
various arrangements of tunneling-coupled quantum dots in order to implement a
transmission function that is superior to the Lorentzian transmission function
of a single quantum dot. We show that the maximum power of the heat engine can
be improved by about a factor of two, even for a small number of dots, by
choosing an optimal structure.Comment: 17 pages, 12 figure
Dynamics of quasiparticles in the two-dimensional Hubbard model
Journal ArticleThe Hubbard model at half-filling is a collective, antiferromagnetic insulator. We study added electrons or holes. The insulating energy gap and the dispersion of the added carriers are calculated variationally in two dimensions with use of a Monte Carlo evaluation of the electronic correlation functions in the insulating phase. Both Eg and m* are found to be temperature dependent
Statistics of stable marriages
In the stable marriage problem N men and N women have to be matched by pairs
under the constraint that the resulting matching is stable. We study the
statistical properties of stable matchings in the large N limit using both
numerical and analytical methods. Generalizations of the model including
singles and unequal numbers of men and women are also investigated.Comment: 7 pages, 6 figures; to appear in Physica
Quasiclassical approach and spin-orbit coupling
We discuss the quasiclassical Green function method for a two-dimensional
electron gas in the presence of spin-orbit coupling, with emphasis on the
meaning of the -integration procedure. As an application of our approach,
we demonstrate how the spin-Hall conductivity, in the presence of spin-flip
scattering, can be easily obtained from the spin-density continuity equation.Comment: 3 pages, Submitted to Physica
Quasiclassical approach to the spin-Hall effect in the two-dimensional electron gas
We study the spin-charge coupled transport in a two-dimensional electron
system using the method of quasiclassical (-integrated) Green's functions.
In particular we derive the Eilenberger equation in the presence of a generic
spin-orbit field. The method allows us to study spin and charge transport from
ballistic to diffusive regimes and continuity equations for spin and charge are
automatically incorporated. In the clean limit we establish the connection
between the spin-Hall conductivity and the Berry phase in momentum space. For
finite systems we solve the Eilenberger equation numerically for the special
case of the Rashba spin-orbit coupling and a two-terminal geometry. In
particular, we calculate explicitly the spin-Hall induced spin polarization in
the corners, predicted by Mishchenko et al. [13]. Furthermore we find universal
spin currents in the short-time dynamics after switching on the voltage across
the sample, and calculate the corresponding spin-Hall polarization at the
edges. Where available, we find perfect agreement with analytical results.Comment: 9 pages, 6 figure
Exact time-dependent density functional theory for impurity models
We employ the density matrix renormalization group to construct the exact
time-dependent exchange correlation potential for an impurity model with an
applied transport voltage. Even for short-ranged interaction we find an
infinitely long-ranged exchange correlation potential which is built up
{instantly} after switching on the voltage. Our result demonstrates the
fundamental difficulties of transport calculations based on time-dependent
density functional theory. While formally the approach works, important
information can be missing in the ground-state functionals and may be hidden in
the usually unknown non-equilibrium functionals
The Peierls-Hubbard model at weak coupling
The Peierls-Hubbard model at weak coupling / M. Dzierzawa, C. Mocanu. - In: Journal of physics : Condensed matter. 17. 2005. S. 2663-267