Exotic insulator may hold clue to key mystery of modern physics

December 4, 2016 by Arthur Hirsch
Credit: Petr Kratochvil/Public Domain

Experiments using laser light and pieces of gray material the size of fingernail clippings may offer clues to a fundamental scientific riddle: what is the relationship between the everyday world of classical physics and the hidden quantum realm that obeys entirely different rules?

"We found a particular material that is straddling these two regimes," said N. Peter Armitage, an associate professor of physics at Johns Hopkins University who led the research for the paper just published in the journal Science. Six scientists from Johns Hopkins and Rutgers University were involved in the work on called topological insulators, which can conduct electricity on their atoms-thin surface, but not in their insides.

Topological insulators were predicted in the 1980s, first observed in 2007 and have been studied intensively since. Made from any number of hundreds of elements, these materials have the capacity to show quantum properties that usually appear only at the microscopic level, but here appear in a material visible to the naked eye.

The experiments reported in Science establish these materials as a distinct state of matter "that exhibits macroscopic quantum mechanical effects," Armitage said. "Usually we think of quantum mechanics as a theory of small things, but in this system quantum mechanics is appearing on macroscopic length scales. The experiments are made possible by unique instrumentation developed in my laboratory."

In the experiments reported in Science, dark gray material samples made of the elements bismuth and selenium – each a few millimeters long and of different thicknesses—were hit with "THz" light beams that are invisible to the unaided eye. Researchers measured the reflected light as it moved through the material samples, and found fingerprints of a quantum state of matter.

Specifically, they found that as the light was transmitted through the material, the wave rotated a specific amount, which is related to physical constants that are usually only measureable in atomic scale experiments. The amount fit the predictions of what would be possible in this quantum state.

The results add to scientists' understanding of topological insulators, but also may contribute to the larger subject that Armitage calls "the central question of modern physics": what is the relationship between the macroscopic classical world, and the microscopic world from which it arises?

Scientists since the early 20th century have struggled with the question of how one set of physical laws governing objects above a certain size can co-exist alongside a different set of laws governing the atomic and subatomic scale. How does classical mechanics emerge from , and where is the threshold that divides these realms?

Those questions remain to be answered, but could be part of the solution.

"It's a piece of the puzzle," said Armitage, who worked on the experiments along with Liang Wu, who was a graduate student at Johns Hopkins when the work was done, Maryam Salehi of the Rutgers University Department of Material Science and Engineering, and Nikesh Koirala, Jisoo Moon and Sean Oh of the Rutgers University Department of Physics and Astronomy.

Explore further: The role of statistics in quantum scale observation explains microscale behaviour

More information: L. Wu et al. Quantized Faraday and Kerr rotation and axion electrodynamics of a 3D topological insulator, Science (2016). DOI: 10.1126/science.aaf5541

Related Stories

Breaking the limits of classical physics

June 7, 2012

(Phys.org) -- With simple arguments, researchers show that nature is complicated. Researchers from the Niels Bohr Institute have made a simple experiment that demonstrates that nature violates common sense – the world ...

Researchers forward quest for quantum computing

May 23, 2013

Research teams from UW-Milwaukee and the University of York investigating the properties of ultra-thin films of new materials are helping bring quantum computing one step closer to reality.

Recommended for you

Studying the quantum vacuum: Traffic jam in empty space

January 18, 2017

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by Professor Alfred Leitenstorfer has now shown how to manipulate the ...

Flexible ferroelectrics bring two material worlds together

January 17, 2017

Until recently, "flexible ferroelectrics" could have been thought of as the same type of oxymoronic phrase. However, thanks to a new discovery by the U.S. Department of Energy's (DOE) Argonne National Laboratory in collaboration ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

24volts
not rated yet Dec 11, 2016
So how many atoms does there have to be of a certain material before it switches from using quantum mechanics to classical mechanics?

Scientists seem to be trying all kinds of stuff, couldn't an electron microscope or what ever it is that they use to move single atoms around on a substrate be used to add atoms together until they got a change of mechanics?

Maybe a dumb question but if it's just a matter of numbers, it seems like someone would have tried it by now.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.