74 research outputs found
An off-board quantum point contact as a sensitive detector of cantilever motion
Recent advances in the fabrication of microelectromechanical systems (MEMS)
and their evolution into nanoelectromechanical systems (NEMS) have allowed
researchers to measure extremely small forces, masses, and displacements. In
particular, researchers have developed position transducers with resolution
approaching the uncertainty limit set by quantum mechanics. The achievement of
such resolution has implications not only for the detection of quantum behavior
in mechanical systems, but also for a variety of other precision experiments
including the bounding of deviations from Newtonian gravity at short distances
and the measurement of single spins. Here we demonstrate the use of a quantum
point contact (QPC) as a sensitive displacement detector capable of sensing the
low-temperature thermal motion of a nearby micromechanical cantilever.
Advantages of this approach include versatility due to its off-board design,
compatibility with nanoscale oscillators, and, with further development, the
potential to achieve quantum limited displacement detection.Comment: 5 pages, 5 figure
Three "universal" mesoscopic Josephson effects
1. Introduction
2. Supercurrent from Excitation Spectrum
3. Excitation Spectrum from Scattering Matrix
4. Short-Junction Limit
5. Universal Josephson Effects
5.1 Quantum Point Contact
5.2 Quantum Dot
5.3 Disordered Point Contact (Average supercurrent, Supercurrent
fluctuations)Comment: 21 pages, 2 figures; legacy revie
Coulomb-Regulated Conductance Oscillations in a Disordered Quantum Wire
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Unexpected features of branched flow through high-mobility two-dimensional electron gases
GaAs-based two-dimensional electron gases (2DEGs) show a wealth of remarkable
electronic states, and serve as the basis for fast transistors, research on
electrons in nanostructures, and prototypes of quantum-computing schemes. All
these uses depend on the extremely low levels of disorder in GaAs 2DEGs, with
low-temperature mean free paths ranging from microns to hundreds of microns.
Here we study how disorder affects the spatial structure of electron transport
by imaging electron flow in three different GaAs/AlGaAs 2DEGs, whose mobilities
range over an order of magnitude. As expected, electrons flow along narrow
branches that we find remain straight over a distance roughly proportional to
the mean free path. We also observe two unanticipated phenomena in
high-mobility samples. In our highest-mobility sample we observe an almost
complete absence of sharp impurity or defect scattering, indicated by the
complete suppression of quantum coherent interference fringes. Also, branched
flow through the chaotic potential of a high-mobility sample remains stable to
significant changes to the initial conditions of injected electrons.Comment: 22 pages, 4 figures, 1 tabl
Universal Resistances of the Quantum RC circuit
We examine the concept of universal quantized resistance in the AC regime
through the fully coherent quantum RC circuit comprising a cavity (dot)
capacitively coupled to a gate and connected via a single spin-polarized
channel to a reservoir lead. As a result of quantum effects such as the Coulomb
interaction in the cavity and global phase coherence, we show that the charge
relaxation resistance is identical for weak and large transmissions and
it changes from to when the frequency (times ) exceeds
the level spacing of the cavity; is the Planck constant and the
electron charge. For large cavities, we formulate a correspondence between the
charge relaxation resistance and the Korringa-Shiba relation of the
Kondo model. Furthermore, we introduce a general class of models, for which the
charge relaxation resistance is universal. Our results emphasize that the
charge relaxation resistance is a key observable to understand the dynamics of
strongly correlated systems.Comment: 12 pages, 3 figure
Quantum Point Contacts and Coherent Electron Focusing
I. Introduction
II. Electrons at the Fermi level
III. Conductance quantization of a quantum point contact
IV. Optical analogue of the conductance quantization
V. Classical electron focusing
VI. Electron focusing as a transmission problem
VII. Coherent electron focusing (Experiment, Skipping orbits and magnetic
edge states, Mode-interference and coherent electron focusing)
VIII. Other mode-interference phenomenaComment: #3 of a series of 4 legacy reviews on QPC'
Temperature Dependence of Spin-Split Peaks in Transverse Electron Focusing
We present experimental results of transverse electron-focusing measurements performed using n-type GaAs. In the
presence of a small transverse magnetic field (B⊥), electrons are focused from the injector to detector leading to
focusing peaks periodic in B⊥. We show that the odd-focusing peaks exhibit a split, where each sub-peak represents a
population of a particular spin branch emanating from the injector. The temperature dependence reveals that the
peak splitting is well defined at low temperature whereas it smears out at high temperature indicating the
exchange-driven spin polarisation in the injector is dominant at low temperatures
Shot noise in mesoscopic systems
This is a review of shot noise, the time-dependent fluctuations in the
electrical current due to the discreteness of the electron charge, in small
conductors. The shot-noise power can be smaller than that of a Poisson process
as a result of correlations in the electron transmission imposed by the Pauli
principle. This suppression takes on simple universal values in a symmetric
double-barrier junction (suppression factor 1/2), a disordered metal (factor
1/3), and a chaotic cavity (factor 1/4). Loss of phase coherence has no effect
on this shot-noise suppression, while thermalization of the electrons due to
electron-electron scattering increases the shot noise slightly. Sub-Poissonian
shot noise has been observed experimentally. So far unobserved phenomena
involve the interplay of shot noise with the Aharonov-Bohm effect, Andreev
reflection, and the fractional quantum Hall effect.Comment: 37 pages, Latex, 10 figures (eps). To be published in "Mesoscopic
Electron Transport," edited by L. P. Kouwenhoven, G. Schoen, and L. L. Sohn,
NATO ASI Series E (Kluwer Academic Publishing, Dordrecht
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