Scientists Discover Bizarre Material Where Electrons Stand Still

New research validates a guided discovery method for 3D flatband materials.

Rice University scientists 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 disrupt the movement of electrons and lock them in place. Did.

This discovery is natural physics. The paper also describes the theoretical design principles and experimental methods that led the research team to this material. 1 part copper, 2 parts vanadium, 4 parts sulfur, alloy It features a 3D pyrochlore lattice composed of corner-sharing tetrahedra.

Quantum entanglement and electron localization

“We’re looking for materials where there may be new states of matter or new exotic features that haven’t been discovered yet,” says study co-author and experimental physicist at Rice. Ming Yi said.

Quantum materials may be of interest, especially if they host strong electronic interactions that cause quantum entanglement. Entanglement causes strange electronic behavior, such as blocking the movement of electrons and locking them in place.

“This quantum interference effect is similar to a wave rippling across the surface of a pond and hitting it head-on,” Yi said. “Collisions create standing waves that do not move. In the case of geometrically frustrated lattice materials, it is the electron wave features that destructively interfere.”

Jianwei Huang, a postdoctoral fellow at Rice University, used the same experimental setup he used to perform angle-resolved photoemission spectroscopy experiments on copper-vanadium alloys. Experiments show that this alloy is the first material known to have a 3D crystal structure and strong quantum interactions that impede the movement of electrons and lock them in place, resulting in a flat electronic band. was shown.Credit: Jeff Fitlow/Rice University

The localization of electrons in metals and metalloids produces flat electronic bands, or flat bands. In recent years, physicists have discovered that the geometrical arrangement of atoms in some 2D crystals, such as the Kagome lattice, can also produce flat bands. New research provides empirical evidence of the effect in 3D materials.

Advanced technology and surprising discoveries

Using an experimental technique called angle-resolved photoelectron spectroscopy (ARPES), Yi and study lead author Jianwei Huang, a postdoctoral fellow in her lab, detailed the band structure of the copper-vanadium-sulfur material. I looked into it and discovered that it hosts a flat band. It’s unique in several ways.

“We found that both types of physics are important in this material,” Yi said. “There was an aspect of geometrical frustration there, as the theory predicted. A pleasant surprise was that there were also correlation effects that produced flat bands at the Fermi level, which were active in determining the physical properties.” It’s about being able to be involved.”

Huang Jianwei.Credit: Jeff Fitlow/Rice University

In solid materials, electrons occupy quantum states that are divided into bands. These electronic bands can be imagined as rungs on a ladder, and electrostatic repulsion forces limit the number of electrons that can occupy each rung. The Fermi level is an inherent property of a material and an important factor in determining band structure, and refers to the energy level of the highest occupied position on the ladder.

Theoretical insights and future directions

Kimiao Shih, a theoretical physicist at Rice and co-corresponding author of the study, said his research group has shown that copper-vanadium alloys and their pyrochlore crystal structures can overcome frustration effects due to geometry and strong electronic interactions. They identified a possible host of combinations and likened the discovery to the discovery of a new continent. .

“This is not only the first study to actually show cooperation between geometric and interactional frustrations, but also the next step of having electrons reside in the same space at the top of the (energy) ladder. “We also show that these stages are most likely to be reorganized into interesting and potentially functional new stages,” Si said.

He said the predictive methodology and design principles his group used in their work could also be useful to theorists studying quantum materials with other crystal lattice structures.

“Pyrochlore is not the only game in town,” says Shi. “This is a new design principle that allows theorists to predictively identify materials where strong electronic correlations give rise to flat bands.”

Yi said there is also plenty of room for further experimental exploration of pyrochlore crystals.

“This is just the tip of the iceberg,” she says. “It’s 3D and it’s new. Given how many amazing discoveries have been made with the Kagome lattice, I think there may be similar or even more exciting discoveries with pyrochlore materials. I imagine it.”

Reference: “Non-Fermi liquid behavior in correlated flatband pyrochlore lattices” Jianwei Huang, Lei Chen, Yuefei Huang, Chandan Setty, Bin Gao, Yue Shi, Zhaoyu Liu, Yichen Zhang, Turgut Yilmaz, Elio Vescovo, Makoto Hashimoto, Donghui Lu, Boris I. Yakobson, Pengcheng Dai, Jiun-Haw Chu, Qimiao Si, Ming Yi, January 26, 2024. natural physics.
DOI: 10.1038/s41567-023-02362-3

The research team included 10 Rice researchers from four laboratories. Physicist Pengcheng Dai’s research group created many samples needed for experimental validation, and Boris Yakobson’s research group from the Department of Materials Science and Nanoengineering quantified flat-band effects caused by geometric frustration. We performed first-principles calculations to The ARPES experiment was conducted at the Rice facility and at the Stanford Synchrotron Radiation Source at SLAC National Accelerator Laboratory in California and the National Synchrotron Source II at Brookhaven National Laboratory in New York, and the team included SLAC, Brookhaven, and U.S. collaborators. University of Washington.

This research used resources supported by a Department of Energy (DOE) contract (DE-AC02-76SF00515) with SLAC, the Gordon and Betty Moore Foundation’s Quantum Systems Emergent Phenomena Initiative (GBMF9470), and funding from Robert A. Welch. Supported by a grant. Foundation (C-2175, C-1411, C-1839), Department of Energy Office of Basic Energy Sciences (DE-SC0018197), Air Force Office of Scientific Research (FA9550-21-1-0343, FA9550-21-1-) 0356), National Science Foundation (2100741), Office of Naval Research (ONR) (N00014-22-1-2753), and the Vannevar Bush Faculty Fellows Program (ONR-VB) N00014-23-1- of the Defense Basic Research Agency managed by ONR. 2870).