The quantum spin Hall effect is a fundamental property of light

June 25, 2015, RIKEN
Credit: Petr Kratochvil/public domain

In a paper that crystalizes knowledge from a variety of experiments and theoretical developments, scientists from the RIKEN Center for Emergent Matter Science in Japan have demonstrated that the quantum spin Hall effect—an effect known to take place in solid state physics—is also an intrinsic property of light.

Photons have neither mass nor charge, and so behave very differently from their massive counterparts, but they do share a property, called spin, which results in remarkable geometric and topological phenomena. The spin—a measure of the intrinsic angular momentum—can be thought of as an equivalent of the spin of a top. In the research published in Science, the team found that photons share with electrons a property related to spin—the Hall effect.

"We had previously done work looking at evanescent electromagnetic waves," says Konstantin Bliokh, who led the research, "and we realized the remarkable properties we found, an unusual transverse spin—was a manifestation of the fact that free-space light exhibits an intrinsic quantum spin Hall effect, meaning that evanescent waves with opposite spins will travel in opposite directions along an interface between two media."

Evanescent waves propagate along the surface of materials, such as metals, at the interface with a vacuum, in the same way that ocean waves emerge at the interface between the air and the water, and they decay exponentially as they move away from the interface.

The quantum spin Hall effect for electrons allows for the existence of an unusual type of material—called a topological insulator—which conducts electricity on the surface but not through the bulk of the material. The team was intrigued to learn that an analogy for these can be found for photons. Though light does not propagate through metals, it is known that it can propagate along interfaces between a metal and vacuum, in the form of so-called surface plasmons involving evanescent light waves. The group was able to show that the unusual transverse spin they found in was actually caused by the intrinsic quantum Hall effect of photons, and their findings also explain recent experiments that have shown spin-controlled unidirectional propagation of surface optical modes.

Bliokh continues, "On a purely scientific level, this research deepens our understanding of the classical theory of light waves developed by James Clark Maxwell 150 years ago, and it could also lead to applications using optical devices that are based on the direction of spin."

Franco Nori, who organized the project, says, "This work was made possible by the interdisciplinary nature of RIKEN, as we were able to bring together discoveries made in several different areas, to show that transverse spin, locked to the direction of propagation of waves, seems to be a universal feature of surface , even when they are of different nature."

Explore further: Extraordinary momentum and spin discovered in evanescent light waves

More information: "Quantum spin Hall effect of light" … 1126/science.aaa9519

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Jun 25, 2015
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5 / 5 (1) Jun 30, 2015
It's nice to see further confirmation of what I've been saying all along.
I'm still holding out hope that science will one day venture to propose that the atomic particles are just long strands of light spinning as a spiral around an axis and that the opposite spins produce electrons and protons (which when combined - as I've heard theorised in science circles too - form neutrons). Maybe one day. Ah well it's nice to at least see my theories getting more new publication as time goes by; so maybe science will deduce this too someday?
not rated yet Jun 30, 2015
It's nice to see further confirmation of what I've been saying all along.

Weird. I checked your comments and you have said nothing of the sort, ever.

not rated yet Jul 01, 2015
Most of my comments have been made elsewhere. I've spoken of my spiral theory of energy. Also I've spoken about my theory that our 'universe' is matter because we are the result of spin mostly of one type and that in one direction there is a corresponding 'universe' that is antimatter because it has the opposite spin to us from the same source. It has been seen that the galaxies have an uncanny alignment and my theory has been proposed recently by 'legitimate' scientists. I've said a lot of things that science sadly explains away. Such as how light switches show a similarity to charged particles. But science has developed the art of explaining away similarities by parallelism. To my mind if it looks like a duck and quacks like a duck there's a good chance it is a duck.
not rated yet Jul 01, 2015
Weird. I checked your comments and you have said nothing of the sort, ever.

That's an intelligent contribution, right?


To my mind if it looks like a duck and quacks like a duck there's a good chance it is a duck.

A reference to Jean Tate ( usage of similar verbiage, not personally ), right?

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