MIT Physicists Catch Two Electron Waves Forming Like Water and Ice in a Quantum Material

Physicists at MIT have found that two different patterns of electron organization can form by completely different processes within the same quantum material, offering a new way to study how such coexisting "phases" arise. The findings, led by Nuh Gedik, the Donner Professor of Physics at MIT, were published in Nature Physics.

The team studied erbium tritelluride, a rare-earth material whose electrons normally spread evenly through it. When cooled to -8 degrees Celsius, the electrons organize into a wave-like pattern called a charge density wave (CDW), in which some regions hold more electrons than others. Cooling the material further, to -113 degrees Celsius, produces a second CDW running at a right angle to the first, and together the two form a checkerboard-like arrangement.

To see how each wave forms, the researchers cooled samples — grown by collaborators at Stanford University — to about -230 degrees Celsius, where both CDWs coexist. They then used one laser pulse to break apart the checkerboard pattern and a second, precisely timed pulse to observe how it reformed. The first CDW reappeared gradually across the whole material, similar to liquid water turning to vapor. The second CDW instead began in isolated patches that grew outward, resembling ice crystals forming in liquid water.

"The mechanism responsible for the emergence of this second phase has long been debated, and our approach provides a powerful new way to uncover the hidden physics behind phase transitions in quantum materials," Gedik said. Co-author Alfred Zong, who co-led the study as an MIT graduate student and is now an assistant professor at Stanford, said the experiment offers "a very neat way to study these multiple phases" in materials that combine superconductivity, magnetism and other electronic behaviors.