Inside many advanced materials, several exotic electronic behaviors — superconductivity, magnetism, charge order — tend to show up together, and physicists have long struggled to explain why. A new MIT experiment offers a clue: watching two competing electronic phases form inside the same crystal in real time, researchers found the two processes follow completely different physical rules, even though both involve the same basic type of electron order.
The team, led by physics professor Nuh Gedik, studied erbium tritelluride, a rare-earth material that develops a wavelike pattern of electron density — called a charge density wave — at about -8°C, then a second wave at about -113°C running perpendicular to the first, together forming an atomic-scale checkerboard. The study, published in Nature Physics, cooled the material to roughly -230°C, where both waves coexist, then used a pair of laser pulses to disrupt and track them.
"This is how we 'shake' and then 'listen' to the system," Gedik said of the technique, described in MIT's account of the findings: a first pulse knocked out the checkerboard pattern, and a second, higher-energy pulse ejected electrons so their energy and momentum could be measured as the pattern reformed.
The dominant wave came back smoothly and uniformly, the kind of gradual transition seen when liquid water evaporates into vapor. The weaker, subdominant wave behaved nothing like that. "We see the destroying of these phases, and then if we wait long enough, they come back," Gedik said. "And depending on how you hit them, the two phases respond differently." Instead of reforming everywhere at once, the second wave nucleated in isolated pockets that then expanded outward — the same process by which liquid water freezes into ice.
A simpler stand-in for superconductivity
Charge density waves are useful to physicists precisely because they are easier to study than the more famous phenomenon they resemble. "Just like superconductivity, charge density waves are a collective phenomena where electrons move together in certain ways," said Yifan Su, the study's lead author. "The power of CDWs is that they are a much simpler form of matter compared to superconductivity."
Co-author Alfred Zong, now at Stanford, framed the stakes more broadly: "People believe the cornerstone of replacing silicon lies in quantum materials that have multiple coexisting phases. Our experiment provides a very neat way to study these multiple phases." Untangling how competing electronic orders form and interact, the team argues, is a step toward engineers eventually being able to design materials with electronic behavior tuned to order — including the kind that underlies future quantum devices.