Skip to main content

A Counterintuitive Set of Tunneling Effects Observed at Last

 



Graphene is the setting for the first demonstration of relativistic electrons’ paradoxical ability to whiz through a barrier, provided the barrier is high enough.

If an electron in a material has a speed that is independent of its energy and if it encounters a barrier head on, it can tunnel straight through. Derived by theorist Oskar Klein in 1929, this counterintuitive finding remained little tested in the lab because it is hard to make electrons approach a barrier head on and to stop them scattering off the edges of the sample. Now Mirza Elahi of the University of Virginia and his collaborators have observed evidence of Klein tunneling in monolayer graphene. What’s more, they also observed the opposite effect, anti-Klein tunneling, in bilayer graphene. In anti-Klein tunneling, head-on electrons do not tunnel at all, while others approaching the barrier at an intermediate angle do.

Graphene’s hexagonal lattice can be thought of as two identical interpenetrating triangular sublattices. One consequence of that view is that graphene’s charge carriers—electrons that hop between the two sublattices—behave as if massless and relativistic at low energies. Another consequence is that the two sublattices bestow on the electrons a chiral property, pseudospin, that resembles spin, which controls the nature of the transmission across the barrier.

To be sure that they were observing Klein or anti-Klein tunneling, Elahi and his collaborators needed to eliminate undesirable edge scattering. They did so by fashioning their graphene layers into so-called Corbino disks, the circular analogs of Hall bars. Such disks are effectively edgeless because the Hall effect turns radial currents flowing out of the disk center into circular currents at the disk perimeter. Through an applied field, the team diverted the circular trajectories so that the electrons encountered the edge barrier head on. The magnetic field also revealed the Klein and anti-Klein tunneling’s pseudospin fingerprints, which appeared as a nontrivial dependence on the azimuthal angle of the tunneling electrons’ outward trajectories. Specifically, the researchers observed, as predicted, a peak in the zero-angle Klein transmission and a dip in the anti-Klein transmission, with an intermediate peak reminiscent of the Brewster angle used in optics to design polarizers.


Comments

Post a Comment

Popular posts from this blog

Physicists observe a new form of magnetism for the first time

MIT physicists have demonstrated a new form of magnetism that could one day be harnessed to build faster, denser, and less power-hungry " spintronic " memory chips. The new magnetic state is a mash-up of two main forms of magnetism: the ferromagnetism of everyday fridge magnets and compass needles, and antiferromagnetism, in which materials have magnetic properties at the microscale yet are not macroscopically magnetized. Now, the MIT team has demonstrated a new form of magnetism , termed "p-wave magnetism." Physicists have long observed that electrons of atoms in regular ferromagnets share the same orientation of "spin," like so many tiny compasses pointing in the same direction. This spin alignment generates a magnetic field, which gives a ferromagnet its inherent magnetism. Electrons belonging to magnetic atoms in an antiferromagnet also have spin, although these spins alternate, with electrons orbiting neighboring atoms aligning their spins antiparalle...
Post a Comment
Read more

"Explore the Fourth Dimension"

Fourth Dimension   The fourth dimension is a fascinating concept that has captured the imaginations of scientists, mathematicians, and artists for centuries. Unlike our three-dimensional world, which is limited by the linear flow of time, the fourth dimension is a realm of space and time that exists beyond our everyday experience. One way to visualize the fourth dimension is through the use of a hypercube, also known as a tesseract. A hypercube is a cube within a cube, with additional lines and edges connecting the vertices of the two cubes. It's impossible to construct in our three-dimensional world, but it provides a glimpse into what the fourth dimension might look like. Another way to understand the fourth dimension is through the concept of a wormhole, a theoretical passage through space-time that connects two distant points in the universe. A wormhole is like a shortcut through the fabric of space-time, allowing us to travel vast distances in an instant. While there is no de...
Post a Comment
Read more

Green comet to pass Earth, won't be back for another 50,000 years

   visit:  https://hep-conferences.sciencefather.com/ After travelling from the icy reaches of our Solar System it will come closest to the Sun on January 12 and pass nearest to Earth on February 1.   A newly discovered comet could be visible to the naked eye as it shoots past Earth and the Sun in the coming weeks for the first time in 50,000 years, astronomers have said. The comet is called C/2022 E3 (ZTF) after the Zwicky Transient Facility, which first spotted it passing Jupiter in March last year. After travelling from the icy reaches of our Solar System it will come closest to the Sun on January 12 and pass nearest to Earth on February 1. It will be easy to spot with a good pair of binoculars and likely even with the naked eye, provided the sky is not too illuminated by city lights or the Moon. The comet "will be brightest when it is closest to the Earth", Thomas Prince, a physics professor at the California Institute of Technology who works at the Zwicky Transi...
Post a Comment
Read more