Scientists have discovered a strange substance where electrons stand still

New research validates a method for guided detection of flat-scale 3D materials.

Scientists at Rice University have discovered a first-of-its-kind material: a 3D crystalline metal in which quantum correlations and the geometry of the crystal structure combine to thwart the movement of electrons and hold them in place.

The discovery was detailed in a study published in Nature physics. The paper also describes the theoretical design principle and experimental methodology that guided the research team to the material. One part copper, two parts vanadium, and four parts sulfur Alloy It features a 3D pyrochlore lattice consisting of tetrahedrons that share corners.

Quantum entanglement and electron localization

“We are looking for materials that potentially have new states of matter or new exotic features that have not been discovered,” said study co-author Ming Yi, an experimental physicist at Rice.

Quantum materials have the potential to be a place for research, especially if they contain strong electronic interactions that lead to quantum entanglement. Entanglement leads to strange electronic behaviors, including inhibiting the movement of electrons to the point where they become fixed in place.

“This quantum interference effect is like waves rippling across the surface of a pond and meeting head-on,” Yi said. “The collision creates a standing wave that does not move. In the case of geometrically frustrated lattice materials, it is the electronic wave functions that interfere destructively.

Rice University postdoctoral researcher Jianwei Huang shared a laboratory device he used to perform specific angle photoemission spectroscopy experiments on a copper-vanadium alloy. Experiments showed that the alloy is the first known material in which the three-dimensional crystal structure and strong quantum interactions frustrate the movement of electrons and hold them in place, resulting in a flat electron bar. Credit: Jeff Vitello/Rice University

Electron localization in metals and semi-metals produces flat electronic domains, or flatbands. In recent years, physicists have discovered that the geometric arrangement of atoms in some 2D crystals, such as Kagome's lattices, can also produce flat ribbons. The new study provides experimental evidence of the effect in 3D matter.

Advanced techniques and amazing results

Using an experimental technique called angle-resolved photoemission spectroscopy, or ARPES, Ye and the study's lead author Jianwei Huang, a postdoctoral researcher in her lab, detailed the copper-vanadium-sulfur ribbon structure and found that it hosts a flat ribbon that is unique in several ways.

“It turns out that both types of physics are important in this material,” Yee said. “The geometric frustration aspect was there, as the theory predicted. The pleasant surprise was that there were also correlation effects that produced the flat band at the Fermi level, where it could be actively involved in determining the physical properties.”

Jianwei Huang. Credit: Jeff Vitello/Rice University

In a solid, electrons occupy quantum states divided into bands. These electronic bands can be thought of as rungs on a ladder, and electrostatic repulsion limits the number of electrons that can occupy each rung. The Fermi level, an inherent property of materials and a critical property for determining their band structure, refers to the energy level of the highest occupied position on the ladder.

Theoretical insights and future directions

Rice is a theoretical physicist and study co-author Kimiao Si, whose research group identified the copper-vanadium alloy and its pyrochlorine crystal structure as a potential host for co-frustration effects from geometry and strong electronic interactions, likened the discovery to finding a new continent. .

“It's the first work that demonstrates not only this collaboration between engineering frustration and interaction but also the next stage, which is getting the electrons to be in the same space at the top of the (energy) ladder, where there is the maximum opportunity to reorganize them into new phases,” said Si. Interesting and potentially effective.”

He said the predictive methodology or design principle his research group used in the study may also be useful to theorists studying quantum materials with other crystal lattice structures.

“Pyrochlor isn’t the only game in town,” See said. “This is a new design principle that allows theorists to predictively identify materials in which flat bands arise due to strong electronic correlations.”

There is also great scope for further experimental exploration of pyrochlore crystals, Yi said.

“This is just the tip of the iceberg,” she added. “This is three-dimensional, which is new, and given the number of amazing results that have been made in Kagome's networks, I imagine there could be equally or perhaps even more exciting discoveries that can be made in pyrochlore materials.”

Reference: “Non-Fermi Fluid Behavior in a Flat-Scale Pyrochlore Lattice” by Jianwei Huang, Li Chen, Yufei Huang, Chandan Seti, Bin Gao, Yue Shi, Xiaoyu Liu, Yichen Zhang, Turgut Yilmaz, Elio Vescovo, Makoto Hashimoto, Donghui Lou, Boris I. Jacobson, Pingcheng Dai, Jun-Hao Zhou, Kimiao Si and Ming Yi, January 26, 2024, Nature physics.
doi: 10.1038/s41567-023-02362-3

The research team included 10 Rice researchers from four laboratories. Physicist Pingqing Dai's research group produced several samples needed for experimental verification, and Boris Jakobsson's research group in the Department of Materials Science and Nanoengineering performed preliminary calculations that quantify flat-band effects resulting from geometric frustration. The ARPES experiments were conducted at Rice and at the SLAC National Laboratory's Synchrotron Light Source II in California and the Second National Synchrotron Light Source at Brookhaven National Laboratory in New York, and the team included collaborators from SLAC, Brookhaven, and Brookhaven National Institute. University of Washington.

The research used resources supported by a Department of Energy (DOE) contract with SLAC (DE-AC02-76SF00515) and was supported by grants from the Emerging Phenomena in Quantum Systems Initiative of the Gordon and Betty Moore Foundation (GBMF9470) and the Robert A. Welch Foundation. Enterprise (C-2175, C-1411, C-1839), DOE Office of Basic Energy Sciences (DE-SC0018197), Air Force Office of Scientific Research (FA9550-21-1-0343, FA9550-21-1-) 0356 ), the National Science Foundation (2100741), the Office of Naval Research (ONR) (N00014-22-1-2753) and the Vannevar Bush Faculty Fellows Program administered by ONR of the Department of Defense Office of Basic Research (ONR-VB) No. 00014-23- 1-2870).