1,044 research outputs found
Quantum interference in nanometric devices: ballistic transport across arrays of T-shaped quantum wires
We propose that the recently realized T-shaped semiconductor quantum wires
(T-wires) could be exploited as three-terminal quantum interference devices.
T-wires are formed by intersecting two quantum wells (QWs). By use of a
scattering matrix approach and the Landauer-B\"uttiker theory, we calculate the
conductance for ballistic transport in the parent QWs and across the wire
region as a function of the injection energy. We show that different
conductance profiles can be selected by tailoring the widths of the QWs and/or
combining more wires on the scale of the Fermi wavelength. Finally, we discuss
the possibility of obtaining spin-dependent conductance of ballistic holes in
the same structures.Comment: To appear in the 09/15/97 issue of Appl. Phys. Lett. (9 pages in
REVTEX + 2 figures in postscript
Strong exciton binding in quantum structures through remote dielectric confinement
We propose a new type of hybrid systems formed by conventional semiconductor
nanostructures with the addition of remote insulating layers, where the
electron-hole interaction is enhanced by combining quantum and dielectric
confinement over different length scales. Due to the polarization charges
induced by the dielectric mismatch at the semiconductor/insulator interfaces,
we show that the exciton binding energy can be more than doubled. For
conventional III-V quantum wires such remote dielectric confinement allows
exciton binding at room temperature.Comment: 4 pages, 3 PostScript figures embedded, best printed in color. Uses
RevTex, multicol, and psfig styles. To appear in Phys. Rev. Let
Wigner crystallization in quantum electron bilayers
The phase diagram of quantum electron bilayers in zero magnetic field is
obtained using density functional theory. For large electron densities the
system is in the liquid phase, while for smaller densities the liquid may
freeze (Wigner crystallization) into four different crystalline phases; the
lattice symmetry and the critical density depend on the the inter-layer
distance. The phase boundaries between different Wigner crystals consist of
both first and second order transitions, depending on the phases involved, and
join the freezing curve at three different triple points.Comment: To appear in Europhys. Lett. (11 pages in REVTEX + 2 figures in
postscript
First Principles Calculations of Charge and Spin Density Waves of sqr3-Adsorbates on Semiconductors
We present ab-initio electronic structure results on the surface of sqr3
adsorbates. In particular, we address the issue of metal-insulator
instabilities, charge-density-waves (CDWs) or spin-density-waves (SDWs), driven
by partly filled surface states and their 2D Fermi surface, and/or by the onset
of magnetic instabilities. The focus is both on the newly discovered
commensurate CDW transitions in the Pb/Ge(111) and Sn/Ge(111) structures, and
on the puzzling semiconducting behavior of the Pb/Ge(111), K/Si(111):B and
SiC(0001) surfaces. In all cases, the main factor driving the instability
appears to be an extremely narrow surface state band. We have carried out so
far preliminary calculations for the Si/Si(111) surface, chosen as our model
system, within the gradient corrected local density (LDA+GC) and local spin
density (LSD+GC) approximations, with the aim of understanding the possible
interplay between 2D Fermi surface and electron correlations in the surface +
adsorbate system. Our spin- unrestricted results show that the sqr3
paramagnetic surface is unstable towards a commensurate SDW with periodicity
3x3 and magnetization 1/3.Comment: 9 pages, 4 Postscript figures, to be published in Surf. Sc
Raman signatures of classical and quantum phases in coupled dots: A theoretical prediction
We study electron molecules in realistic vertically coupled quantum dots in a
strong magnetic field. Computing the energy spectrum, pair correlation
functions, and dynamical form factor as a function of inter-dot coupling via
diagonalization of the many-body Hamiltonian, we identify structural
transitions between different phases, some of which do not have a classical
counterpart. The calculated Raman cross section shows how such phases can be
experimentally singled out.Comment: 9 pages, 2 postscript figures, 1 colour postscript figure, Latex 2e,
Europhysics Letters style and epsfig macros. Submitted to Europhysics Letter
Valence band spectroscopy in V-grooved quantum wires
We present a combined theoretical and experimental study of the anisotropy in
the optical absorption of V-shaped quantum wires. By means of realistic band
structure calculations for these structures, we show that detailed information
on the heavy- and light-hole states can be singled out from the anisotropy
spectra {\em independently of the electron confinement}, thus allowing accurate
valence band spectroscopy.Comment: To be published in Appl. Phys. Lett. (8 pages in REVTeX, two
postscipt figures
The mechanism for the 3 x 3 distortion of Sn/ge (111)
We show that two distinct ground states, one nonmagnetic,
metallic, and distorted, the other magnetic, semimetallic (or insulating) and
undistorted, compete in -phase adsorbates on semiconductor (111)
surfaces. In Sn/Ge(111), LSDA/GGA calculations indicate, in agreement with
experiment, that the distorted metallic ground state prevails. The reason for
stability of this state is analysed, and is traced to a sort of bond density
wave, specifically a modulation of the antibonding state filling between the
adatom and a Ge-Ge bond directly underneath
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