Rice University scientists have discovered a first-of-its-kind material, a 3D crystalline metal by which quantum correlations and the geometry of the crystal structure mix to frustrate the movement of electrons and lock them in place.
The find is 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 fabric. One part copper, two parts vanadium and 4 parts sulfur, the alloy contains a 3D pyrochlore lattice consisting of corner-sharing tetrahedra.
“We search for materials where there are potentially latest states of matter or latest exotic features that have not been discovered,” said study co-corresponding writer Ming Yi, a Rice experimental physicist.
Quantum materials are a possible place to look, especially in the event that they host strong electron interactions that give rise to quantum entanglement. Entanglement results in strange electronic behaviors, including frustrating the movement of electrons to the purpose where they change into locked in place.
“This quantum interference effect is analogous to waves rippling across the surface of a pond and meeting head-on,” Yi said. “The collision creates a standing wave that doesn’t move. Within the case of geometrically frustrated lattice materials, it is the electronic wave functions that destructively interfere.”
Electron localization in metals and semimetals produces flat electronic bands, or flat bands. Lately, physicists have found that the geometric arrangement of atoms in some 2D crystals, like Kagome lattices, also can produce flat bands. The brand new study provides empirical evidence of the effect in a 3D material.
Using an experimental technique called angle-resolved photoemission spectroscopy, or ARPES, Yi and study lead writer Jianwei Huang, a postdoctoral researcher in her lab, detailed the band structure of the copper-vanadium-sulfur material and located it hosted a flat band that is exclusive in several ways.
“It seems that each sorts of physics are essential on this material,” Yi said. “The geometric frustration aspect was there, as theory had predicted. The nice surprise was that there have been also correlation effects that produced the flat band on the Fermi level, where it may well actively take part in determining the physical properties.”
In solid-state matter, electrons occupy quantum states which might be divided in bands. These electronic bands might be imagined as rungs on a ladder, and electrostatic repulsion limits the variety of electrons that may occupy each rung. Fermi level, an inherent property of materials and a vital one for determining their band structure, refers back to the energy level of the best occupied position on the ladder.
Rice theoretical physicist and study co-corresponding writer Qimiao Si, whose research group identified the copper-vanadium alloy and its pyrochlore crystal structure as being a possible host for combined frustration effects from geometry and robust electron interactions, likened the invention to finding a brand new continent.
“It is the very first work to essentially show not only this cooperation between geometric- and interaction-driven frustration, but additionally the subsequent stage, which is getting electrons to be in the identical space at the highest of the (energy) ladder, where there is a maximal likelihood of their reorganizing into interesting and potentially functional latest phases,” Si said.
He said the predictive methodology or design principle that his research group utilized in the study may additionally prove useful to theorists who study quantum materials with other crystal lattice structures.
“The pyrochlore just isn’t the one game on the town,” Si said. “It is a latest design principle that permits theorists to predictively discover materials by which flat bands arise on account of strong electron correlations.”
Yi said there’s also loads of room for further experimental exploration of pyrochlore crystals.
“That is just the tip of the iceberg,” she said. “That is 3D, which is latest, and just given what number of surprising findings there have been on Kagome lattices, I’m envisioning that there may very well be equally or perhaps much more exciting discoveries to be made within the pyrochlore materials.”
The research team included 10 Rice researchers from 4 laboratories. Physicist Pengcheng Dai’s research group produced the various samples needed for experimental verification, and Boris Yakobson’s research group within the Department of Materials Science and NanoEngineering performed first-principle calculations that quantified the flat-band effects produced by geometric frustration. ARPES experiments were conducted at Rice and on the SLAC National Accelerator Laboratory’s Stanford Synchrotron Radiation Lightsource in California and Brookhaven National Laboratory’s National Synchrotron Light Source II in Recent York, and the team included collaborators from SLAC, Brookhaven and the University of Washington.
The research used resources supported by a Department of Energy (DOE) contract to SLAC (DE-AC02-76SF00515) and was supported by grants from the Gordon and Betty Moore Foundation’s Emergent Phenomena in Quantum Systems Initiative (GBMF9470), the Robert A. Welch Foundation (C-2175, C-1411, C-1839), the DOE’s Office of Basic Energy Sciences (DE-SC0018197), the 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 ONR-managed Vannevar Bush Faculty Fellows program of the Department of Defense Basic Research Office (ONR-VB N00014-23-1-2870).
