Quantum Physicists Find Paradoxical Material a Mashup of Three Different Phases at Once – “This Is Uncharted Territory”

 

Credit: Lucy Reading-Ikkanda/Simons Foundation

Materials that look like montages of triangular tiles at the atomic level occasionally have paradoxical properties, and quantum physicists have finally found out why.

 

Using a combination of innovative computational techniques, the researchers found that under special conditions, these triangular-patterned materials can wind up in a mashup of three different phases at the same time. The competing phases overlap, with each fighting for dominance. Consequently, the material counterintuitively becomes more ordered when heated up, the researchers report October 19 in Physical Review X.

 

"This is uncharted territory," says research lead author Alexander Wietek, a study fellow at the Flatiron Institute's Center for Computational Quantum Physics (CCQ) in New York City. "Experimentalists had seen these strange properties, but they didn't know what the individual electrons in the materials were doing. Our role as theorists is to understand from the bottom up what's really happening."

 

The findings could help physicists develop materials for future electronics, Wietek says. This is because the odd properties, he says, are symbolic of an elusive state of matter sought for potential use in error-correcting quantum computing.

 

Wietek's co-authors on the new paper include CCQ research fellow Riccardo Rossi, CCQ research physicist Miles Stoudenmire and CCQ director Antoine Georges.

 

The physicists investigated how the electrons in the materials act. Electrons determine almost all a material's properties, from magnetism to conductivity and even color.

 

Grasping the combined behavior of the electrons is a monumental task. When two particles interact, they become quantum mechanically entangled with one another. Even once they're detached, their fates remain entangled, and they can't be treated separately.

 

An infographic exploring the surprising behavior of electrons in materials with an underlying triangular structure. Credit: Lucy Reading-Ikkanda/Simons Foundation

The behavior of electrons in a material is dependent on the layout of the atoms, and the triangular lattice arrangement is extra-ordinary. That's because electrons have a spin, which can point either up or down. An electron might, such as, want to have a different spin direction than its neighbors. But in a triangle with three atoms and only two spin directions, "someone is always going to be unhappy," Wietek says. "This causes the system to fluctuate because it doesn't really know what to do." Quantum physicists call this 'geometric frustration.'