20,882 research outputs found
Corner overgrowth: Bending a high mobility two-dimensional electron system by 90 degrees
Introducing an epitaxial growth technique called corner overgrowth, we
fabricate a quantum confinement structure consisting of a high-mobility
GaAs/AlGaAs heterojunction overgrown on top of an ex-situ cleaved substrate
corner. The resulting corner-junction quantum-well heterostructure effectively
bends a two-dimensional electron system (2DES) at an atomically sharp angle. The high-mobility 2DES demonstrates fractional quantum Hall effect
on both facets. Lossless edge-channel conduction over the corner confirms a
continuum of 2D electrons across the junction, consistent with
Schroedinger-Poisson calculations of the electron distribution. This growth
technique differs distinctly from cleaved-edge overgrowth and enables a
complementary class of new embedded quantum heterostructures.Comment: 3 pages, 4 figures, latest version accepted to AP
The Amplitude Mode in the Quantum Phase Model
We derive the collective low energy excitations of the quantum phase model of
interacting lattice bosons within the superfluid state using a dynamical
variational approach. We recover the well known sound (or Goldstone) mode and
derive a gapped (Higgs type) mode that was overlooked in previous studies of
the quantum phase model. This mode is relevant to ultracold atoms in a strong
optical lattice potential. We predict the signature of the gapped mode in
lattice modulation experiments and show how it evolves with increasing
interaction strength.Comment: 4 pages, 3 figure
HIV/AIDS, Security and Conflict: New Realities, New Responses
Ten years after the HIV/AIDS epidemic itself was identified as a threat to international peace and security, findings from the three-year AIDS, Security and Conflict Initiative (ASCI)(1) present evidence of the mutually reinforcing dynamics linking HIV/AIDS, conflict and security
Generation and detection of spin-orbit coupled neutron beams
Spin-orbit coupling of light has come to the fore in nano-optics and
plasmonics, and is a key ingredient of topological photonics and chiral quantum
optics. We demonstrate a basic tool for incorporating analogous effects into
neutron optics: the generation and detection of neutron beams with coupled spin
and orbital angular momentum. He neutron spin-filters are used in
conjunction with specifically oriented triangular coils to prepare neutron
beams with lattices of spin-orbit correlations, as demonstrated by their
spin-dependant intensity profiles. These correlations can be tailored to
particular applications, such as neutron studies of topological materials
Probing the Electrostatics of Integer Quantum Hall Edges with Momentum-Resolved Tunnel Spectroscopy
We present measurements of momentum-resolved magneto-tunneling from a
perpendicular two-dimensional (2D) contact into integer quantum Hall (QH) edges
at a sharp edge potential created by cleaved edge overgrowth. Resonances in the
tunnel conductance correspond to coincidences of electronic states of the QH
edge and the 2D contact in energy-momentum space. With this dispersion relation
reflecting the potential distribution at the edge we can directly measure the
band bending at our cleaved edge under the influence of an external voltage
bias. At finite bias we observe significant deviations from the flat-band
condition in agreement with self-consistent calculations of the edge potential
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