125 research outputs found
Quantum wells with atomically smooth interfaces
By a cleaved-edge overgrowth method with molecular beam epitaxy and a (110)
growth-interrupt-anneal, we have fabricated a GaAs quantum well exactly 30
monolayers thick bounded by atomically smooth AlGaAs hetero-interfaces without
atomic roughness. Micro-photoluminescence imaging of this quantum well indeed
shows spatially uniform and spectrally sharp emission over areas of several
tens of m in extent. By adding a fractional GaAs monolayer to our quantum
well we are able to study the details of the atomic step-edge kinetics
responsible for flat interface formation.Comment: 4 pages, 3 figures, revTex
One-dimensional continuum and exciton states in quantum wires
High-quality T-shaped quantum wires are fabricated by cleaved-edge overgrowth
with the molecular beam epitaxy on the interface improved by a growth-interrupt
high-temperature anneal. Characterization by micro-photoluminescence (PL) and
PL excitation (PLE) spectroscopy at 5 K reveals high uniformity, a sharp
spectral width, and a small Stokes shift of one-dimensional (1-D) excitons. The
PLE spectrum for 1-D states shows a large peak of ground-state excitons and a
small absorption band ascribed to 1-D continuum states with an onset at 11 meV
above the exciton peak.Comment: 4 pages, 4 figures, RevTe
Lasing from a single quantum wire
A laser with an active volume consisting of only a single quantum wire in the
1-dimensional (1-D) ground state is demonstrated. The single wire is formed
quantum-mechanically at the T-intersection of a 14 nm Al_{0.07}Ga_{0.93}As
quantum well and a 6 nm GaAs quantum well, and is embedded in a 1-D single-mode
optical waveguide. We observe single-mode lasing from the quantum wire ground
state by optical pumping. The laser operates from 5 to 60 K, and has a low
threshold pumping power of 5 mW at 5 K.Comment: 4 pages including 4 figure
Particle-hole symmetric Luttinger liquids in a quantum Hall circuit
We report current transmission data through a split-gate constriction
fabricated onto a two-dimensional electron system in the integer quantum Hall
(QH) regime. Split-gate biasing drives inter-edge backscattering and is shown
to lead to suppressed or enhanced transmission, in marked contrast with the
expected linear Fermi-liquid behavior. This evolution is described in terms of
particle-hole symmetry and allows us to conclude that an unexpected class of
gate-controlled particle-hole-symmetric chiral Luttinger Liquids (CLLs) can
exist at the edges of our QH circuit. These results highlight the role of
particle-hole symmetry on the properties of CLL edge states.Comment: 4 pages, 4 figure
Observation of collapse of pseudospin order in bilayer quantum Hall ferromagnets
The Hartree-Fock paradigm of bilayer quantum Hall states with finite
tunneling at filling factor =1 has full pseudospin ferromagnetic order
with all the electrons in the lowest symmetric Landau level. Inelastic light
scattering measurements of low energy spin excitations reveal major departures
from the paradigm at relatively large tunneling gaps. The results indicate the
emergence of a novel correlated quantum Hall state at =1 characterized by
reduced pseudospin order. Marked anomalies occur in spin excitations when
pseudospin polarization collapses by application of in-plane magnetic fields.Comment: ReVTeX4, 4 pages, 3 EPS figure
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