1,738 research outputs found
Diffusive Transport in Quasi-2D and Quasi-1D Electron Systems
Quantum-confined semiconductor structures are the cornerstone of modern-day
electronics. Spatial confinement in these structures leads to formation of
discrete low-dimensional subbands. At room temperature, carriers transfer among
different states due to efficient scattering with phonons, charged impurities,
surface roughness and other electrons, so transport is scattering-limited
(diffusive) and well described by the Boltzmann transport equation. In this
review, we present the theoretical framework used for the description and
simulation of diffusive electron transport in quasi-two-dimensional and
quasi-one-dimensional semiconductor structures. Transport in silicon MOSFETs
and nanowires is presented in detail.Comment: Review article, to appear in Journal of Computational and Theoretical
Nanoscienc
Exact few-body results for strongly correlated quantum gases in two dimensions
The study of strongly correlated quantum gases in two dimensions has
important ramifications for understanding many intriguing pheomena in solid
materials, such as high- superconductivity and the fractional quantum
Hall effect. However, theoretical methods are plagued by the existence of
significant quantum fluctuations. Here, we present two- and three-body exact
solutions for both fermions and bosons trapped in a two-dimensional harmonic
potential, with an arbitrary -wave scattering length. These few-particle
solutions link in a natural way to the high-temperature properties of
many-particle systems via a quantum virial expansion. As a concrete example,
using the energy spectrum of few fermions, we calculate the second and third
virial coefficients of a strongly interacting Fermi gas in two dimensions, and
consequently investigate its high-temperature thermodynamics. Our thermodynamic
results may be useful for ongoing experiments on two-dimensional Fermi gases.
These exact results also provide an unbiased benchmark for quantum Monte Carlo
simulations of two-dimensional Fermi gases at high temperatures.Comment: 11 pages, 6 figure
Dynamics of trapped two-component Fermi gas: temperature dependence of the transition from collisionless to collisional regime
We develop a numerical method to study the dynamics of a two-component atomic
Fermi gas trapped inside a harmonic potential at temperature T well below the
Fermi temperature Tf. We examine the transition from the collisionless to the
collisional regime down to T=0.2 Tf and find good qualitative agreement with
the experiments of B. DeMarco and D.S. Jin [Phys. Rev. Lett. vol. 88, 040405
(2002)]. We demonstrate a twofold role of temperature on the collision rate and
on the efficiency of collisions. In particular we observe an hitherto
unreported effect, namely that the transition to hydrodynamic behavior is
shifted towards lower collision rates as temperature decreases.Comment: 4 pages, 3 figure
Strongest atomic physics bounds on Non-Commutative Quantum Gravity Models
Investigations of possible violations of the Pauli Exclusion Principle
represent critical tests of the microscopic space-time structure and
properties. Space-time non-commutativity provides a class of universality for
several Quantum Gravity models. In this context the VIP-2 Lead experiment sets
the strongest bounds, searching for Pauli Exclusion Principle violating
atomic-transitions in lead, excluding the -Poincar\'e Non Commutative
Quantum Gravity models far above the Planck scale for non-vanishing
``electric-like'' components, and up to
Planck scales if .Comment: 7 pages, 2 figure
Time-of-Flight Measurements as a Possible Method to Observe Anyonic Statistics
We propose a standard time-of-flight experiment as a method for observing the
anyonic statistics of quasiholes in a fractional quantum Hall state of
ultracold atoms. The quasihole states can be stably prepared by pinning the
quasiholes with localized potentials and a measurement of the mean square
radius of the freely expanding cloud, which is related to the average total
angular momentum of the initial state, offers direct signatures of the
statistical phase. Our proposed method is validated by Monte Carlo calculations
for and fractional quantum Hall liquids containing a realistic
number of particles. Extensions to quantum Hall liquids of light and to
non-Abelian anyons are briefly discussed.Comment: Title change, enhanced Supplemental Material, almost published
version (to appear in Phys. Rev. Lett.
String patterns in the doped Hubbard model
Understanding strongly correlated quantum many-body states is one of the most
difficult challenges in modern physics. For example, there remain fundamental
open questions on the phase diagram of the Hubbard model, which describes
strongly correlated electrons in solids. In this work we realize the Hubbard
Hamiltonian and search for specific patterns within the individual images of
many realizations of strongly correlated ultracold fermions in an optical
lattice. Upon doping a cold-atom antiferromagnet we find consistency with
geometric strings, entities that may explain the relationship between hole
motion and spin order, in both pattern-based and conventional observables. Our
results demonstrate the potential for pattern recognition to provide key
insights into cold-atom quantum many-body systems.Comment: 8+28 pages, 5+10 figure
A Generalized Variational Principle with Applications to Excited State Mean Field Theory.
We present a generalization of the variational principle that is compatible with any Hamiltonian eigenstate that can be specified uniquely by a list of properties. This variational principle appears to be compatible with a wide range of electronic structure methods, including mean field theory, density functional theory, multireference theory, and quantum Monte Carlo. Like the standard variational principle, this generalized variational principle amounts to the optimization of a nonlinear function that, in the limit of an arbitrarily flexible wave function, has the desired Hamiltonian eigenstate as its global minimum. Unlike the standard variational principle, it can target excited states and select individual states in cases of degeneracy or near-degeneracy. As an initial demonstration of how this approach can be useful in practice, we employ it to improve the optimization efficiency of excited state mean field theory by an order of magnitude. With this improved optimization, we are able to demonstrate that the accuracy of the corresponding second-order perturbation theory rivals that of singles-and-doubles equation-of-motion coupled cluster in a substantially broader set of molecules than could be explored by our previous optimization methodology
- …