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Stacked Layers of Atom-thin Material Reveal Complex Physical Phenomena

Physicists have long tried to study how groups of quantum particles interact in the hopes of better understanding elusive phenomena like high-temperature superconductivity and magnetism. Imagine a pinball game – but rather than one metal ball, there are billions or more, all ricocheting chaotically off each other and their surroundings.

A collaboration led by Cornell University that includes physicist Allan MacDonald at The University of Texas at Austin, reports in the journal Nature the successful demonstration of a physical model that reveals some of the ways that these particles interact.

One classic method to study such systems is to create a simplified model, called a Hubbard model, that can capture the essence of these particle interactions. The solution to the model, however, only exists in one dimension. For decades, physicists have tried to realize the Hubbard model in two or three dimensions by creating quantum simulators that can mimic it.

In 2018, MacDonald theorized a Hubbard model simulator would be possible by stacking two atomic monolayers of semiconductors such that they overlap to make a moiré pattern. The team successfully built just such a physical model from layers of tungsten disulfide and tungsten diselenide.

So far, they have used the simulator to make two significant discoveries. First, they observed a Mott insulating state, whereby materials that should behave like metals and conduct electricity instead function like insulators – a phenomenon that physicists predicted the Hubbard model would demonstrate. Second, they mapped the system’s magnetic phase diagram, a way of representing phases that the material goes through as certain paramaters, such as temperature and external magnetic field, vary.

The project is led by Kin Fai Mak, associate professor of physics at Cornell. The research was primarily supported by the U.S. Department of Energy.

This post is adapted from a press release by Cornell University.

Saturday Physics Workshop, April 4th 2020

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