38,143 research outputs found
Polariton Bose-Einstein condensate at room temperature in a Al(Ga)N nanowire-dielectric microcavity with a spatial potential trap
A spatial potential trap is formed in a 6.0 {\mu}m Al(Ga)N nanowire by
varying the Al composition along its length during epitaxial growth. The
polariton emission characteristics of a dielectric microcavity with the single
nanowire embedded in-plane has been studied at room temperature. Excitation is
provided at the Al(Ga)N end of the nanowire and polariton emission is observed
from the lowest bandgap GaN region of the nanowire. Comparison of the results
with those measured in an identical microcavity with an uniform GaN nanowire
and having an identical exciton-photon detuning suggests evaporative cooling of
the polaritons as they are transported across the trap in the Al(Ga)N nanowire.
Measurement of the spectral characteristics of the polariton emission, their
momentum distribution, first-order spatial coherence and time-resolved
measurements of polariton cooling provide strong evidence of the formation of
an equilibrium Bose-Einstein condensate, a unique state of matter in solid
state systems, in the GaN region of the nanowire, at room temperature. An
equilibrium condensate is not formed in the GaN nanowire dielectric microcavity
without the spatial potential trap.Comment: 28 pages, 6 figures, Submitted to the Proceedings of the National
Academy of Sciences of the United States of Americ
Polarization Properties of Single Quantum Dots in Nanowires
We study the absorption and emission polarization of single semiconductor
quantum dots in semiconductor nanowires. We show that the polarization of light
absorbed or emitted by a nanowire quantum dot strongly depends on the
orientation of the nanowire with respect to the directions along which light is
incident or emitted. Light is preferentially linearly polarized when directed
perpendicular to the nanowire elongation. In contrast, the degree of linear
polarization is low for light directed along the nanowire. This result is vital
for photonic applications based on intrinsic properties of quantum dots, such
as generation of entangled photons. As an example, we demonstrate optical
access to the spin states of a single nanowire quantum dot.Comment: 4 pages, 4 figure
Imaging a 1-electron InAs quantum dot in an InAs/InP nanowire
Nanowire heterostructures define high-quality few-electron quantum dots for
nanoelectronics, spintronics and quantum information processing. We use a
cooled scanning probe microscope (SPM) to image and control an InAs quantum dot
in an InAs/InP nanowire, using the tip as a movable gate. Images of dot
conductance vs. tip position at T = 4.2 K show concentric rings as electrons
are added, starting with the first electron. The SPM can locate a dot along a
nanowire and individually tune its charge, abilities that will be very useful
for the control of coupled nanowire dots
Absorbing/Emitting Phonons with one dimensional MOSFETs
We consider nanowires in the field effect transistor device configuration.
Modeling each nanowire as a one dimensional lattice with random site
potentials, we study the heat exchanges between the nanowire electrons and the
substrate phonons, when electron transport is due to phonon-assisted hops
between localized states. Shifting the nanowire conduction band with a metallic
gate induces different behaviors. When the Fermi potential is located near the
band center, a bias voltage gives rise to small local heat exchanges which
fluctuate randomly along the nanowire. When it is located near one of the band
edges, the bias voltage yields heat currents which flow mainly from the
substrate towards the nanowire near one boundary of the nanowire, and in the
opposite direction near the other boundary. This opens interesting perspectives
for heat management at submicron scales: Arrays of parallel gated nanowires
could be used for a field control of phonon emission/absorption.Comment: 9 pages, 11 figure
Epitaxial growth of aligned semiconductor nanowire metamaterials for photonic applications
A novel class of optical metamaterials is presented consisting of high densities of aligned gallium phosphide (GaP) nanowires fabricated using metal-organic vapor phase-epitaxy. Starting from a gold island film as a catalyst for nanowire growth, a sequential combination of vapor-liquid-solid and lateral growth modes is employed to obtain a continuous tunability of the nanowire volume fraction from 7% to over 35%. By choosing different crystallographic orientations of the GaP substrate, metamaterials are designed with different nanowire orientations. The anisotropy of the nanowire building blocks results in strong optical birefringence. Polarization interferometry demonstrates a very large polarization extinction contrast of 4 × 103 combined with a sharp angular resonance which holds promise for optical sensing. Nanowire metamaterials may find applications in photonics, optoelectronics, non-linear and quantum optics, microfluidics, bio-, and gas sensing
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