348 research outputs found
Coherent exciton transport in semiconductors
We review the topic of Bose-Einstein condensation of excitons in
semiconductors, focusing on the signatures of the macroscopic order of the
exciton condensate.Comment: Some references were updated with respect to the published version.
appears as Chapter 19 in Novel Superfluids Volume 2, edited by K. H.
Bennemann and J. B. Ketterson, International Series of Monographs on Physics
no. 157, pages 423-474 (Oxford University Press, Oxford, 2014
Thermoelectric properties of junctions between metal and strongly correlated semiconductor
We propose a junction of metal and rare-earth compound semiconductor as the
basis for a possible efficient low-temperature thermoelectric device. If an
overlayer of rare earth atoms differing from the bulk is placed at the
interface, very high values of the figure of merit ZT can be reached at low
temperature. This is due to sharp variation of the transmission coefficient of
carriers across the junction at a narrow energy range, which is intrinsically
linked to the localized character of the overlayer f-orbital.Comment: RevTeX 3.0, 4 pages, 3 postscript figures. To be published in Applied
Physics Letter
Synchronization of Coupled Boolean Phase Oscillators
We design, characterize, and couple Boolean phase oscillators that include
state-dependent feedback delay. The state-dependent delay allows us to realize
an adjustable coupling strength, even though only Boolean signals are
exchanged. Specifically, increasing the coupling strength via the range of
state-dependent delay leads to larger locking ranges in uni- and bi-directional
coupling of oscillators in both experiment and numerical simulation with a
piecewise switching model. In the unidirectional coupling scheme, we unveil
asymmetric triangular-shaped locking regions (Arnold tongues) that appear at
multiples of the natural frequency of the oscillators. This extends
observations of a single locking region reported in previous studies. In the
bidirectional coupling scheme, we map out a symmetric locking region in the
parameter space of frequency detuning and coupling strength. Because of large
scalability of our setup, our observations constitute a first step towards
realizing large-scale networks of coupled oscillators to address fundamental
questions on the dynamical properties of networks in a new experimental
setting.Comment: 8 pages, 8 figure
Ultra-high-frequency piecewise-linear chaos using delayed feedback loops
We report on an ultra-high-frequency (> 1 GHz), piecewise-linear chaotic
system designed from low-cost, commercially available electronic components.
The system is composed of two electronic time-delayed feedback loops: A primary
analog loop with a variable gain that produces multi-mode oscillations centered
around 2 GHz and a secondary loop that switches the variable gain between two
different values by means of a digital-like signal. We demonstrate
experimentally and numerically that such an approach allows for the
simultaneous generation of analog and digital chaos, where the digital chaos
can be used to partition the system's attractor, forming the foundation for a
symbolic dynamics with potential applications in noise-resilient communications
and radar
Full configuration interaction approach to the few-electron problem in artificial atoms
We present a new high-performance configuration interaction code optimally
designed for the calculation of the lowest energy eigenstates of a few
electrons in semiconductor quantum dots (also called artificial atoms) in the
strong interaction regime. The implementation relies on a single-particle
representation, but it is independent of the choice of the single-particle
basis and, therefore, of the details of the device and configuration of
external fields. Assuming no truncation of the Fock space of Slater
determinants generated from the chosen single-particle basis, the code may
tackle regimes where Coulomb interaction very effectively mixes many
determinants. Typical strongly correlated systems lead to very large
diagonalization problems; in our implementation, the secular equation is
reduced to its minimal rank by exploiting the symmetry of the effective-mass
interacting Hamiltonian, including square total spin. The resulting Hamiltonian
is diagonalized via parallel implementation of the Lanczos algorithm. The code
gives access to both wave functions and energies of first excited states.
Excellent code scalability in a parallel environment is demonstrated; accuracy
is tested for the case of up to eight electrons confined in a two-dimensional
harmonic trap as the density is progressively diluted and correlation becomes
dominant. Comparison with previous Quantum Monte Carlo simulations in the
Wigner regime demonstrates power and flexibility of the method.Comment: RevTeX 4.0, 18 pages, 6 tables, 9 postscript b/w figures. Final
version with new material. Section 6 on the excitation spectrum has been
added. Some material has been moved to two appendices, which appear in the
EPAPS web depository in the published versio
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