4 research outputs found
On the lower bound on the exchange-correlation energy in two dimensions
We study the properties of the lower bound on the exchange-correlation energy
in two dimensions. First we review the derivation of the bound and show how it
can be written in a simple density-functional form. This form allows an
explicit determination of the prefactor of the bound and testing its tightness.
Next we focus on finite two-dimensional systems and examine how their distance
from the bound depends on the system geometry. The results for the high-density
limit suggest that a finite system that comes as close as possible to the
ultimate bound on the exchange-correlation energy has circular geometry and a
weak confining potential with a negative curvature
Spin-dependent thermoelectric transport coefficients in near-perfect quantum wires
Thermoelectric transport coefficients are determined for semiconductor
quantum wires with weak thickness fluctuations. Such systems exhibit anomalies
in conductance near 1/4 and 3/4 of 2e^2/h on the rising edge to the first
conductance plateau, explained by singlet and triplet resonances of conducting
electrons with a single weakly bound electron in the wire [T. Rejec, A. Ramsak,
and J.H. Jefferson, Phys. Rev. B 62, 12985 (2000)]. We extend this work to
study the Seebeck thermopower coefficient and linear thermal conductance within
the framework of the Landauer-Buettiker formalism, which also exhibit anomalous
structures. These features are generic and robust, surviving to temperatures of
a few degrees. It is shown quantitatively how at elevated temperatures thermal
conductance progressively deviates from the Wiedemann-Franz law.Comment: To appear in Phys. Rev. B 2002; 3 figure