Researchers at University of Michigan Engineering have discovered that electron crystals, also known as charge density waves, accumulate defects as they melt, a process similar to the way physical solids transition from ordered structures to liquids. This finding challenges the conventional understanding of quantum structures as inherently ordered, revealing a continuum of disorder that could be harnessed for new technologies. “Our work shows that these quantum structures, often thought to have a highly ordered structure, actually span a continuum of disorder that could be leveraged to engineer and control these materials,” said Robert Hovden, associate professor of materials science and engineering and corresponding author of the study published in Matter. Hovden suggests quantum metallurgy could be a future direction, explaining that controlling these defects could enable both superconductors and devices mimicking the function of artificial neurons.
Electron Crystals Exhibit Defects During Melting Process
Electron crystals, typically envisioned as highly ordered quantum structures, surprisingly accumulate defects as they transition from a crystalline state to a disordered one, a behavior mirroring metallurgical processes observed in conventional solids. This finding expands understanding of how these quantum systems respond to changes in temperature and pressure, revealing a continuum of disorder previously unappreciated. Detecting this melting involved firing an electron beam at the metal while heated to 568 degrees Fahrenheit; the resulting diffraction patterns revealed smearing and fading of electron cluster positions as defects accumulated. Researchers identified similar diffraction patterns indicative of melting in a review of 28 prior studies of charge density waves across both two-dimensional and several three-dimensional metals, suggesting this behavior is widespread.
This universality is promising, as Jeremy Shen, a U-M master’s student and co-first author, noted: “The fact that we have one universal control across all these systems that we could use to access different properties is very exciting.” Hovden explained that metallurgists often control defects in metals to produce specific properties, and a similar approach might help harness the potential of quantum materials in future devices. The ability to control this degree of “melting” could lead to novel devices, including superconductors and components for neuromorphic computing.
Tantalum Sulfide Used to Observe Charge Density Wave Behavior
Researchers are increasingly focused on manipulating the subtle arrangements of electrons within materials to create novel devices, and recent work at University of Michigan Engineering has revealed surprising behavior in these so-called electron crystals, or charge density waves. These structures, exhibiting a periodic clustering of electrons, were observed to accumulate defects as they undergo a phase transition analogous to melting in conventional solids; this challenges prior assumptions of inherent order within quantum systems. The team, led by Robert Hovden, utilized tantalum sulfide as a model material to observe this “melting” process, employing an electron beam while heating the metal to 568 degrees Fahrenheit to track changes in the electron crystal’s structure. Detecting this structural change involved observing how electrons deflected off the atoms, creating diffraction patterns that revealed the deformation of electron clusters.
The team’s analysis of 28 studies across various metals exhibiting charge density waves found evidence of melting in nearly every two-dimensional metal, as well as several three-dimensional metals. This discovery is not merely an observation; researchers are actively exploring the potential to control the degree of this “melting”, an approach similar to how metallurgists control defects in metals to produce specific properties, to engineer materials with tailored properties.
Our work shows that these quantum structures, which are often thought to have a highly ordered structure, actually span a continuum of disorder that could be leveraged to engineer and control these materials.
Electron Diffraction Reveals Intermediate Melting States
This discovery, published in Matter, stems from observations of charge density waves, neatly arranged clusters of electrons, within tantalum sulfide heated to 568 degrees Fahrenheit while firing an electron beam. This universality suggests a broad applicability for manipulating these electron crystals. “Metallurgists often control defects, or disorder, in metals to produce specific properties,” Hovden said. “A similar approach might help us harness the potential of quantum materials in future devices, suggesting that controlling defects could provide a universal framework for manipulating these materials.”
When you look at these materials, they can have very different electrical and magnetic properties, but we can describe the core underlying physics of most of their charge density waves with this rather simple framework.
Universal Framework Connects Charge Density Wave Properties Across Metals
The potential to engineer materials with tailored electrical properties is expanding thanks to a newly identified universality in how electron crystals melt, a phenomenon with implications for both superconductivity and neuromorphic computing. This universality is significant because it provides a framework, similar to how metallurgists control defects, for controlling material properties. The ability to manipulate the degree of this “melting” could allow for the creation of materials that seamlessly switch between conducting and insulating states, a crucial capability for building more efficient and energy-conscious computing systems.
Metallurgists often control defects, or disorder, in metals to produce specific properties.
