MIT physicists discover electrons rebuilding like ice inside a quantum material

MIT physicists have uncovered new insights into how two distinct forms of electron organization can coexist within a single quantum material. Their findings, published in Nature Physics, could enhance our understanding of materials that exhibit superconductivity, magnetism, and other electronic phases. This knowledge could lead to the development of more powerful quantum devices.

The researchers investigated erbium tritelluride, a rare-earth material known for its unusual electronic behavior. At room temperature, electrons are evenly distributed throughout the material. However, when cooled to specific temperatures, the electrons begin to arrange themselves into a wave-shaped arrangement called a charge density wave (CDW) phase. Cooling the material even further results in a second wave pattern.

The first CDW phase emerges gradually, akin to liquid water turning into vapor. The second phase, however, develops in isolated regions that expand outward, similar to ice crystals forming in liquid water. This behavior has long puzzled physicists, but the MIT team's approach offers a powerful new method to uncover the hidden physics behind these phase transitions in quantum materials.

The study's lead author, Yifan Su, explains that charge density waves are a collective phenomenon where electrons move together in specific ways. They are a simpler form of matter compared to superconductivity, providing a playground for fundamental understanding. The researchers were particularly interested in a material that can support two CDW phases simultaneously.

Understanding how these two phases appear and coexist could offer clues about the more complicated phase transitions seen in superconductivity and other unusual electronic states. The MIT team cooled erbium tritelluride to extremely low temperatures, allowing both CDW phases to coexist in a checkerboard arrangement.

The researchers used two timed laser pulses to disrupt the electronic pattern and observe how the two waves returned. The first laser pulse served as the "shake," breaking apart the checkerboard of charge density waves. A subsequent pulse of high-energy photons then knocked electrons out of the material. By measuring the energy and momentum of the expelled electrons at different intervals after the first pulse, the researchers could analyze how each phase developed.