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Related Concept Videos

Continuous Charge Distributions01:17

Continuous Charge Distributions

Imagine a bucket of water. It contains many molecules, of the order of 1026 molecules. Thus, although it contains discrete elements (molecules) at the microscopic level, macroscopically, it can be considered continuous. Small volume elements of water, infinitesimal compared to the bulk of the bucket's volume, still contain many molecules. Under this framework, quantized matter is approximated as continuous for practical purposes.
The electric charge can also be subjected to an analogical...
Calculation of Electric Flux01:25

Calculation of Electric Flux

Consider the electric field of an oppositely charged, parallel-plate system and an imaginary box between those plates. Let the bottom face of the box be ABCD, and the top face be FGHK. The electric field between the plates is uniform and points from the positive plate toward the negative plate. The calculation of this field's flux through the box's various faces shows that the net flux through the box is zero. Why does the flux cancel out here?
Magnetic Force Between Two Parallel Currents01:13

Magnetic Force Between Two Parallel Currents

Two long, straight, and parallel current-carrying conductors exert a force of equal magnitude on one another. The direction of the force depends on the current direction in the conductors.
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Magnetic Field Of A Current Loop01:16

Magnetic Field Of A Current Loop

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Induced Electric Fields01:23

Induced Electric Fields

The fact that emfs are induced in circuits implies that work is being done on the conduction electrons in the wires. What can possibly be the source of this work? We know that it’s neither a battery nor a magnetic field, as a battery does not have to be present in a circuit where current is induced, and magnetic fields never do any work on moving charges. The source of the work is in fact an electric field that is induced in the wires. For example, if a stationary conductor is placed in a...
Induced Electric Fields: Applications01:27

Induced Electric Fields: Applications

An important distinction exists between the electric field induced by a changing magnetic field and the electrostatic field produced by a fixed charge distribution. Specifically, the induced electric field is nonconservative because it does not work in moving a charge over a closed path. In contrast, the electrostatic field is conservative and does no net work over a closed path. Hence, electric potential can be associated with the electrostatic field but not the induced field. The following...

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Updated: Jun 29, 2026

Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F−
06:53

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Published on: July 27, 2018

Imaging coherent electron flow from a quantum point contact

Topinka1, LeRoy, Shaw

  • 1Division of Engineering and Applied Sciences, Department of Physics, and Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA. Materials Department, University of California, Santa Barbara, CA 93106, USA.

Science (New York, N.Y.)
|September 29, 2000
PubMed
Summary
This summary is machine-generated.

Researchers imaged coherent electron flow in a quantum point contact using a charged tip. This technique visualizes electron behavior and conductance quantization in nanostructures.

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Area of Science:

  • Condensed Matter Physics
  • Quantum Mechanics
  • Nanotechnology

Background:

  • Two-dimensional electron gases (2DEGs) in semiconductor nanostructures exhibit quantum phenomena.
  • Quantum point contacts (QPCs) are crucial for studying electron transport at the nanoscale.
  • Understanding electron flow in confined systems is essential for future electronics.

Purpose of the Study:

  • To develop a method for imaging coherent electron flow in QPCs.
  • To experimentally verify theoretical predictions of conductance quantization.
  • To investigate the role of individual electron modes in quantum transport.

Main Methods:

  • Utilized scanning probe microscopy with a charged tip to probe a 2DEG in a GaAs/AlGaAs heterostructure.
  • Operated at liquid helium temperatures to maintain quantum coherence.
  • Varied the width of the QPC to observe changes in electrical conductance.

Main Results:

  • Successfully imaged coherent electron flow from the lowest quantized modes of the QPC.
  • Observed electrical conductance increasing in quantized steps of 2 e(2)/h as QPC width increased.
  • Detected interference fringes separated by half the electron wavelength, confirming theoretical predictions.
  • Demonstrated that localized tip-induced perturbations selectively reduced conductance in specific channels.

Conclusions:

  • The charged tip scanning technique provides real-space imaging of electron wave functions in QPCs.
  • Experimental results strongly support theoretical models of quantum transport and conductance quantization.
  • This method allows for the manipulation and study of individual electron conduction channels.