3,931 research outputs found
Quantum simulation of a Fermi-Hubbard model using a semiconductor quantum dot array
Interacting fermions on a lattice can develop strong quantum correlations,
which lie at the heart of the classical intractability of many exotic phases of
matter. Seminal efforts are underway in the control of artificial quantum
systems, that can be made to emulate the underlying Fermi-Hubbard models.
Electrostatically confined conduction band electrons define interacting quantum
coherent spin and charge degrees of freedom that allow all-electrical
pure-state initialisation and readily adhere to an engineerable Fermi-Hubbard
Hamiltonian. Until now, however, the substantial electrostatic disorder
inherent to solid state has made attempts at emulating Fermi-Hubbard physics on
solid-state platforms few and far between. Here, we show that for gate-defined
quantum dots, this disorder can be suppressed in a controlled manner. Novel
insights and a newly developed semi-automated and scalable toolbox allow us to
homogeneously and independently dial in the electron filling and
nearest-neighbour tunnel coupling. Bringing these ideas and tools to fruition,
we realize the first detailed characterization of the collective Coulomb
blockade transition, which is the finite-size analogue of the
interaction-driven Mott metal-to-insulator transition. As automation and device
fabrication of semiconductor quantum dots continue to improve, the ideas
presented here show how quantum dots can be used to investigate the physics of
ever more complex many-body states
Estimates of electronic interaction parameters for LaO compounds (=Ti-Ni) from ab-initio approaches
We have analyzed the ab-initio local density approximation band structure
calculations for the family of perovskite oxides, LaO with =Ti-Ni
within a parametrized nearest neighbor tight-binding model and extracted
various interaction strengths. We study the systematics in these interaction
parameters across the transition metal series and discuss the relevance of
these in a many-body description of these oxides. The results obtained here
compare well with estimates of these parameters obtained via analysis of
electron spectroscopic results in conjunction with the Anderson impurity model.
The dependence of the hopping interaction strength, t, is found to be
approximately .Comment: 18 pages; 1 tex file+9 postscript files (appeared in Phys Rev B Oct
15,1996
Dissipationless transport in low density bilayer systems
In a bilayer electronic system the layer index may be viewed as the
z-component of an isospin-1/2. An XY isospin-ordered ferromagnetic phase was
observed in quantum Hall systems and is predicted to exist at zero magnetic
field at low density. This phase is a superfluid for opposite currents in the
two layers. At B=0 the system is gapless but superfluidity is not destroyed by
weak disorder. In the quantum Hall case, weak disorder generates a random gauge
field which probably does not destroy superfluidity. Experimental signatures
include Coulomb drag and collective mode measurements.Comment: 4 pages, no figures, submitted to Phys. Rev. Let
Variation in oil and its major constituents due to season and stage of the crop in Java citronella (Cymhopogon winterianus Jowitt.)
Variations in citronella oil and its major constituents due to seasonal changes and stage of the crop were studied for three years under the climatic conditions of Jorhat, Assam. Rainfall, temperature .. sunshine and relative humidity have cumulative effect on the oil yield and its major constituents namely, citronellal, citronellol and geraniol. Post monsoon months were seemed to be favourable, contributing higher oil yield. Citronellal content was higher during September (44.3%) and October (45.7%). It was observed that light rainfall (100 to 200 mm), moderate temperature (20-30oC), sunshine hours of 5 to 6 hours and high humidity (90-95%) wet:e the favourable meteorological ,parameters for higher oil yield and citronellal content in citronella oiL Growing period or stage of crop growth also had profound effect on the oil yield and citronellal content. Older crop with highly matured leaves found to yield higher oil and less citronella!. Alcohol content in citronella oil was not affected by seasonal variation. However, total alcohol percentage was found to reduce, while aldehyde percentage increased.
 
Summarizing and measuring development activity
Software developers pursue a wide range of activities as part of their work, and making sense of what they did in a given time frame is far from trivial as evidenced by the large number of awareness and coordination tools that have been developed in recent years. To inform tool design for making sense of the information available about a developer's activity, we conducted an empirical study with 156 GitHub users to investigate what information they would expect in a summary of development activity, how they would measure development activity, and what factors in uence how such activity can be condensed into textual summaries or numbers. We found that unexpected events are as important as expected events in summaries of what a developer did, and that many developers do not believe in measuring development activity. Among the factors that in uence summarization and measurement of development activity, we identified development experience and programming languages.Christoph Treude, Fernando Figueira Filho, Uirá Kulesz
Disorder and Interaction in 2D: Exact diagonalization study of the Anderson-Hubbard-Mott model
We investigate, by numerically calculating the charge stiffness, the effects
of random diagonal disorder and electron-electron interaction on the nature of
the ground state in the 2D Hubbard model through the finite size exact
diagonalization technique. By comparing with the corresponding 1D Hubbard model
results and by using heuristic arguments we conclude that it is
\QTR{it}{unlikely} that there is a 2D metal-insulator quantum phase transition
although the effect of interaction in some range of parameters is to
substantially enhance the non-interacting charge stiffness.Comment: 13 pages, 2 figures Revised version. Accepted for publication in
Phys. Rev. Let
Inelastic lifetimes of confined two-component electron systems in semiconductor quantum wire and quantum well structures
We calculate Coulomb scattering lifetimes of electrons in two-subband quantum
wires and in double-layer quantum wells by obtaining the quasiparticle
self-energy within the framework of the random-phase approximation for the
dynamical dielectric function. We show that, in contrast to a single-subband
quantum wire, the scattering rate in a two-subband quantum wire contains
contributions from both particle-hole excitations and plasmon excitations. For
double-layer quantum well structures, we examine individual contributions to
the scattering rate from quasiparticle as well as acoustic and optical plasmon
excitations at different electron densities and layer separations. We find that
the acoustic plasmon contribution in the two-component electron system does not
introduce any qualitatively new correction to the low energy inelastic
lifetime, and, in particular, does not produce the linear energy dependence of
carrier scattering rate as observed in the normal state of high-
superconductors.Comment: 16 pages, RevTeX, 7 figures. Also available at
http://www-cmg.physics.umd.edu/~lzheng
Manifestation of the magnetic depopulation of one-dimensional subbands in the optical absorption of acoustic magnetoplasmons in side-gated quantum wires
We have investigated experimentally and theoretically the far-infrared (FIR)
absorption of gated, deep-mesa-etched GaAs/AlGaAs quantum wires. To
overcome Kohn's theorem we have in particular prepared double-layered wires and
studied the acoustic magnetoplasmon branch. We find oscillations in the
magnetic-field dispersion of the acoustic plasmon which are traced back to the
self-consistently screened density profile in its dependence on the magnetic
depopulation of the one-dimensional subbands.Comment: LaTeX-file, 4 pages with 3 included ps-figures, to appear in Physica
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