Two phases, two rebuilding paths: MIT physicists watch electrons reassemble in erbium tritelluride

Two distinct rebuilding mechanisms

The MIT team, led by Nuh Gedik (the Donner Professor of Physics at MIT), used a "pump-probe" technique: they hit the ErTe₃ sample with an ultrafast laser pulse to momentarily disrupt both CDW phases, then watched with a second pulse how the electrons reorganized over time . What they saw was unexpected.

• The dominant CDW phase rebuilt uniformly and gradually — a classic, continuous (second-order) phase transition, analogous to liquid water evaporating into vapor .
• The subdominant (second) CDW phase rebuilt in a radically different way: electrons first formed isolated, nanometer-scale pockets of order, which then expanded and merged until the phase was fully restored. This nucleation-and-growth behavior — akin to water crystallizing into ice — had been theorized but never directly observed in this context .

The team used time- and angle-resolved photoemission spectroscopy (trARPES) to capture the electronic structure as it evolved on picosecond timescales, effectively creating a slow-motion movie of the rebuilding process .

Why this matters for superconductivity and quantum devices

The finding is more than a materials-science curiosity. Many of the most promising quantum materials — including those that host high-temperature superconductivity — exhibit multiple coexisting electronic phases. Untangling how these phases compete, coexist, and influence one another is a central challenge in the field .

• A new way to study competing orders: Because the two CDW phases in ErTe₃ rebuild through different mechanisms and on different timescales, researchers can now selectively study each phase by tracking its characteristic recovery signature. This provides a "very neat way to study these multiple phases," as co-author Alfred Zong noted .
• Toward switchable quantum devices: If engineers can selectively perturb one electronic order while leaving others intact, they may be able to switch a material between insulating, conducting, or superconducting states on demand — a core requirement for quantum logic and low-power electronics that go beyond silicon .
• A general experimental strategy: The pump-probe approach demonstrated in ErTe₃ is not limited to this one material. It can be extended to other quantum materials — including those relevant to topological quantum computing — to reveal hidden dynamics of competing orders that are invisible in equilibrium measurements .

Bottom line

This experiment shows that competing electronic phases in a quantum material can have fundamentally different formation mechanisms, and that these mechanisms can be disentangled simply by watching how the phases recover after a laser pulse. The approach gives physicists a powerful new tool to study the complex, cooperative behavior of electrons — and brings us one step closer to engineering materials with precisely controlled electronic properties.