A new study validates a method for controlled unrolling of 3D materials with a flat strip. Scientists at Rice University have discovered a first-of-its-kind material: a three-dimensional crystalline metal in which quantum correlations and the geometry of the crystal structure combine to impede the movement of electrons and lock them in place.

The finding is detailed in a published study. Natural Physics. The article also describes the theoretical design principle and experimental methodology that guided the research team to the material. This alloy, composed of one part copper, two parts vanadium, and four parts sulfur, has a three-dimensional pyrochlore lattice of corner-sharing tetrahedra.

Quantum entanglement and localization of electrons

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

Quantum materials are a likely place to look, especially if they contain strong electronic interactions that lead to quantum entanglement. Entanglement causes electrons to behave strangely; This includes disrupting the movement of electrons to the point where they become locked in place.

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

The localization of electrons in metals and semimetals creates flat electron bands or flat bands. In recent years, physicists have discovered that the geometric arrangement of atoms in some two-dimensional crystals, such as Kagome lattices, can also form flat bands. New research provides empirical evidence for the effect in 3D material.

Advanced methods and unexpected findings

Using an experimental technique called angle-resolved photoemission spectroscopy, or ARPES, Yi and the study’s lead author, Jianwei Huang, a postdoctoral researcher in his lab, detailed the band structure of the copper-vanadium-sulfur material and found that it contained a flat band. is specific to many relationships

“It turns out that both types of physics are important in this material,” Yi said. “There was an element of geometric frustration, just as the theory predicted. A pleasant surprise was that there were also correlation effects that formed a flat band at the Fermi level, where it could play an active role in determining physical properties.”

In a solid, electrons occupy quantum states divided into regions. These electron 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, which is a natural property of materials and is very important for determining band structures, refers to the energy level of the highest position occupied on the ladder.

Theoretical ideas and future directions

Rice, a theoretical physicist, and study co-author Zimiao Xie, whose research team identified the copper-vanadium alloy and its pyrochlore crystal structure as a possible host for the combined effects of geometry blocking and strong electron interaction, likened the discovery to a discovery of the copper-vanadium alloy. new continent.

“This is the first study to really show not only this cooperation between geometric and interaction-induced frustration, but also the next stage, where electrons are in the same space at the top of the (energy) ladder, with the maximum chance of them reorganizing into interesting and potentially functional new stages.” Xi said.

He said the prediction methodology, or design principle, that the research group used in the study could also be useful for theorists working on 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 predictably describe materials in which flat bands arise due to strong electron correlation.”

There’s also plenty of room for further experimental research on pyrochlore crystals, Yee said.

“This is just the tip of the iceberg,” he said. “What’s new is 3D, and given how many amazing discoveries have been made on Kagome’s lattices, I predict that the same, or even more exciting, discoveries can be made in pyrochlore materials.”