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Quantum metallurgy: Electron crystals deform and melt

In a process analogous to how solids melt into liquids, the electrons in many different metals form crystal-like patterns that can deform and melt, opening new pathways for neuromorphic computing and superconductors, University of Michigan Engineering researchers have found. "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," said Robert Hovden, associate professor of materials science and engineering and corresponding author of the study published in Matter. "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. Quantum metallurgy could be the future."

The first direct observation of a liquid charge density wave

Charge density waves (CDWs) are ordered, crystal-like patterns in the arrangement of electrons that spontaneously form inside some solid materials. These patterns can change how electricity flows through materials, in some cases prompting the emergence of superconductivity or other unusual physical states. Physics theories suggest that at certain temperatures CDWs "melt," similarly to how conventional solids transition to a liquid state. So far, however, this transition to a liquid CDW had not yet been observed experimentally. Researchers at University of California Los Angeles (UCLA) have gathered the first direct evidence of a CDW liquid state in the layered transition metal dichalcogenide 1T-TaS2. Their paper, published in Nature Physics, could open new possibilities for the study of hidden electronic phases in correlated physical systems.

Scientists discover method to restore vanishing electronic patterns in quantum materials

A new study published in Nature Communications April 7 could reshape the future of magnetic and electronic technology. Scientists at Rice University have discovered how a disappearing electronic pattern in a quantum material can be revived under specific thermal conditions. The finding opens new doors for customizable quantum materials and in-situ engineering, where devices are manufactured or manipulated directly at their point of use. Led by Pengcheng Dai, the Sam and Helen Worden Professor of Physics and Astronomy, the researchers uncovered the cause behind a vanishing electronic phenomenon in a class of crystalline materials known as kagome lattice, a geometric arrangement of corner-sharing triangles named after a traditional Japanese basket pattern. This discovery reveals how heating methods impact the presence of a charge density wave (CDW), a quantum pattern of electron arrangement, in the kagome metal iron germanide (FeGe). It also demonstrates how its reappearance enhances magnetic and electronic properties.

Physicists identify key mechanism behind chiral charge density wave in TiSe₂

Chirality is a property of some molecules, subatomic particles, living organisms and other physical or biological systems. This property entails a lack of mirror symmetry in these systems' underlying structures. Researchers at Pohang University of Science and Technology, Argonne National Laboratory and other institutes recently carried out a study investigating the origins of chirality in the transition-metal dichalcogenide 1T phase titanium diselenide (1T-TiSe2). Their paper, published in Nature Physics, outlines a key mechanism that contributes to the formation of a chiral charge density wave in this material. "TiSe2 is a material that has been known since 1976 and extensively studied since then," B. J. Kim, senior author of the paper, told Phys.org. "In particular, its crystal structure has been studied in detail and revisited many times, and all previous studies only found consistency with the known structural model.

Researchers unveil pressure-tuned superconductivity in natural bulk heterostructure 6R-TaS₂

By combining comprehensive high-pressure measurements and first-principles calculations, a research group has discovered the pressure-induced unusual evolution of superconductivity (SC) and exotic interplay between SC and charge-density-wave (CDW) order in a natural bulk van der Waals heterostructure. Their research results are published in Physical Review Letters. Engineering van der Waals heterostructures (vdWHs) via pressure in a continuous manner not only allows for generation of new states of matter, but also provides a distinctive platform to study the interplay between competing electronic orders in separated layers. Natural bulk vdWHs 6R-TaS2 incorporates CDW order and SC in distinct 1T- and 1H-TaS2 monolayers and is equivalent to a stack of superconductor-insulator-superconductor Josephson junctions.

Evidence that atomically thin hafnium telluride is an excitonic insulator

The condensation of excitons with non-zero momentum can give rise to so-called charge density waves (CDW). This phenomenon can prompt the transition of materials into a fascinating new quantum phase, known as an excitonic insulator. Researchers at Shanghai Jiao Tong University and other institutes recently carried out a study exploring the possibility that this metal-insulator transition could occur in the atomically thin semi-metallic HfTe2. Their observations, outlined in Nature Physics, unveiled possible excitonic CDW and metal-insulator transitions in the atomically thin material. "The formation of CDW in materials has various mechanisms (e.g., Fermi surface nesting, lattice distortions, etc.) and exclusion of other CDW formation mechanisms is the key to identifying the existence of an excitonic insulator," Peng Chen, corresponding author of the paper, told Phys.org.

Putting a new spin on 1T phase tantalum disulfide: Scientists uncover a hidden electronic state

Research often unfolds as a multistage process. The solution to one question can spark several more, inspiring scientists to reach further and look at the larger problem from several different perspectives. Such projects can often be the catalyst for collaborations that leverage the expertise and capabilities of different teams and institutions as they grow. For half a century, scientists have delved into the mysteries of 1T phase tantalum disulfide (1T-TaS2), an inorganic layered material with some intriguing quantum properties, like superconductivity and charge density waves (CDW). To unlock the complex structure and behavior of this material, researchers from the Jozef Stefan Institute in Slovenia and Université Paris-Saclay in France reached out to experts utilizing the Pair Distribution Function (PDF) beamline at the National Synchrotron Light Source II (NSLS-II), a U.S. Department of Energy (DOE) Office of Science User Facility located at DOE's Brookhaven National Laboratory, to learn more about the material's structure.

Team creates 'quantum composites' for electrical and optical innovations

A team of UCR electrical engineers and material scientists demonstrated a research breakthrough that may result in wide-ranging advancements in electrical, optical, and computer technologies.

The Marlan and Rosemary Bourns College of Engineering research group, led by distinguished professor Alexander Balandin, has shown in the laboratory the unique and practical function of newly created materials, which they called quantum composites.

These composites consist of small crystals of called "charge density wave quantum materials" incorporated within a polymer (large molecules with repeating structures) matrix. Upon heating or light exposure, charge density wave material undergoes a phase transition that leads to an unusual electrical response of the composites.

Compared to other materials that reveal quantum phenomena, the quantum composites created by Balandin's group exhibited functionality at a much wider range of temperatures and had a greatly increased ability to store electricity, giving them an excellent potential for utility.

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