MIT physicists have directly observed and distinguished the emergence processes of two coexisting electronic phases in the rare-earth quantum material erbium tritelluride. Their findings, published in Nature Physics, clarify longstanding questions about how distinct charge density waves (CDWs) can form simultaneously within a single material, revealing one phase’s gradual formation and another’s crystal-like nucleation.
What Happened
The research team, led by Professor Nuh Gedik at MIT, studied erbium tritelluride — a material known to develop two perpendicular charge density waves when cooled to ultra-low temperatures. The first CDW appears near -8°C (-230 K), stretching electrons into a wave along one direction. Upon further cooling to about -113°C (-186 K), a second, subdominant CDW emerges at a right angle, creating a checkerboard-like coexistence of electronic phases.
To investigate how these waves form and recover, the researchers cooled atomically thin erbium tritelluride samples to -230°C (-46 K), where both phases coexist. Using an ultrafast pump-probe technique, they briefly disrupted the CDW states with an initial laser pulse (“shake”) and then monitored recovery via a secondary, timed pulse that knocked electrons out for energy and momentum analysis (“listen”). This approach allowed them to capture time-resolved snapshots of electronic reorganization as the phases reassembled.
Key Facts
The study was published in Nature Physics in 2024, conducted primarily by physicists at MIT with sample synthesis from Stanford collaborators. It focused on erbium tritelluride, a rare-earth layered material that exhibits charge density waves at cryogenic temperatures. The team observed two CDWs — the dominant phase forming gradually across the sample, and the subdominant phase nucleating in pockets that spread like ice crystals. The data were obtained through time- and angle-resolved photoemission spectroscopy (trARPES), which provided detailed measurements of electron momentum and energy as the phases reassembled.
What This Means
This breakthrough sheds light on how competing quantum phases can coexist and influence each other within a complex material — a vital step toward understanding phenomena like superconductivity and magnetism. The discovery that one CDW forms via a textbook gradual phase transition while the other emerges through nucleation challenges previous assumptions that all electron phases arise uniformly.
Understanding the distinct mechanisms underpinning coexisting phases could enable engineers to better control electron behavior in quantum materials, potentially accelerating the development of next-generation electronic devices that leverage unique quantum properties. Moreover, erbium tritelluride serves as a simplified model system, offering insights applicable to more complicated materials where multiple exotic phases intertwine, such as high-temperature superconductors. The findings open avenues for clarifying how electronic phases compete, coexist, or enhance each other — a fundamental question in materials physics.
Background
Charge density waves are collective electron states in which electrons self-organize into waves of alternating high and low density. Commonly observed at ultracold temperatures, CDWs have been studied as simpler counterparts to superconducting and magnetic phases. Erbium tritelluride is known to host two perpendicular CDWs simultaneously, but the dynamics of their formation and coexistence remained unclear prior to this work.
Analysis
According to lead author Yifan Su, the power of studying CDWs lies in their relative simplicity compared to more complex electron states like superconductivity. Professor Gedik emphasized that elucidating why some materials support multiple phases and how those phases interact is crucial to advancing materials science. The team’s work provides a powerful experimental approach to unravel the hidden physics behind phase transitions in quantum materials.
What Remains Unclear
While the study clarifies how the second phase nucleates and expands, questions remain about the precise interactions between the coexisting charge density waves and their influence on other electronic phenomena. The implications for other quantum states like superconductivity await further exploration. The exact role of these phase transitions in determining macroscopic material properties is an open field for future research.
What Comes Next
The researchers plan to apply their ultrafast pump-probe technique to investigate more complex quantum materials exhibiting intertwined phases such as superconductivity and magnetism. Continued experiments aim to deepen understanding of phase competition and cooperation, which could inform the engineering of materials with tailor-made electronic properties. Future work may also involve extending these findings toward practical quantum devices.
Sources
This article is based on reporting and publicly available information from the following sources:
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