Characterization of high-quality material reveals important details relevant to next generation nanoelectronic devices
Quantum mechanics is the field of physics governing the behavior of things on atomic scales, where things work very differently from our everyday world.
This is a dirac cone showing a typical dispersion relation (energy vs. momentum) for 2-D graphene material. Red cross-sectional lines represent quantization of the energy (and momentum) due to a finite size constriction.
Credit: B. Terrés, L. A. Chizhova, F. Libisch, J. Peiro, D. Jörger, S. Engels, A. Girschik, K. Watanabe, T. Taniguchi, S. V. Rotkin, J. Burgdörfer, C. Stampfer
One of the most direct manifestations of quantum mechanics is quantization. Quantization results in the discrete character of physical properties at small scales, which could be the radius of an atomic orbit or the resistance of a molecular wire. The most famous one, which won Albert Einstein the Nobel Prize, is the quantization of the photon energy in the photoelectric effect-- the observation that many metals emit electrons when light shines upon them.
Quantization occurs when a quantum particle is confined to a small space. Its wave function develops a standing wave pattern, like waves in a small puddle. Physicists then speak of size quantization: the energy of the particle may only take those values where the nodal pattern of the standing wave matches the system boundary.
A striking consequence of size quantization is quantized conductance: the number of particles that can simultaneously traverse a narrow corridor, a so-called nanoconstriction, become discrete. As a result the current through such a constriction is an integer multiple of the quantum of conductance.
In a recent joint experimental and theoretical work, an international group of physicists demonstrated size quantization of charge carriers, i.e. quantized conductance in nanoscale samples of graphene. The results have been published in an article called "Size quantization of Dirac fermions in graphene constrictions" in Nature Communications.
The high-quality material graphene, a single-atomic layer of carbon, embedded in hexagonal boron nitride demonstrates unusual physics due to the hexagonal--or honey comb--symmetry of its lattice. However, observing size quantization of charge carriers in graphene nanoconstrictions has, until now, proved elusive due to the high sensitivity of the electron wave to disorder.
The researchers demonstrated quantization effects at very low temperatures (liquid Helium), where the influence of thermal disorder ceases. This new approach--of encapsulating graphene constrictions between layers of boron nitride--allowed for exceptionally clean samples, and thus highly accurate measurements.
At zero magnetic field, the measured current shows clear signatures of size quantization, closely following theoretical predictions. For increasing magnetic field, these structures gradually evolve into the Landau levels of the quantum Hall effect.
"The high sensitivity of this transition to scattering at the constriction edges reveals indispensable details about the role of edge scattering in future graphene nanoelectronic devices," said Slava V. Rotkin, professor of physics and materials science & engineering at Lehigh University and a co-author of the study.
Lori Friedman | EurekAlert!
Robust and functional – surface finishing by suspension spraying
19.09.2017 | Fraunhofer-Institut für Keramische Technologien und Systeme IKTS
Graphene and other carbon nanomaterials can replace scarce metals
19.09.2017 | Chalmers University of Technology
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.
Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...
MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems Holding GmbH about commercial use of a multi-well tissue plate for automated and reliable tissue engineering & drug testing.
MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems...
Pathogenic bacteria are becoming resistant to common antibiotics to an ever increasing degree. One of the most difficult germs is Pseudomonas aeruginosa, a...
Scientists from the MPI for Chemical Energy Conversion report in the first issue of the new journal JOULE.
Cell Press has just released the first issue of Joule, a new journal dedicated to sustainable energy research. In this issue James Birrell, Olaf Rüdiger,...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
19.09.2017 | Event News
19.09.2017 | Physics and Astronomy
19.09.2017 | Power and Electrical Engineering