New research started with a special material that behaves unusually when it's extremely cold — 135 degrees below zero Fahrenheit, close to the most frigid temperature ever recorded in Antarctica — and showed that the unusual behavior could be extended to well above room temperature — up to about 135 F, close to the highest heat ever measured in Death Valley, California.
The base material was a stack of 3-atom-thin sheets made from a compound called tantalum disulfide. The special behavior is known as the commensurate charge density wave (CCDW). In contrast to the usual disorderly motion of electrons in a metal, the CCDW causes them to move together in a pattern that traces the internal structure of the material.
Getting that behavior to persist when it's warm took one surprising step: adding an amino acid — a building block for proteins — called arginine.
The research came from an international collaboration led by investigators at the UCLA College and the California NanoSystems Institute at UCLA (CNSI). The combined material was made of repeated vertical stacks with two layers of arginine sandwiched between single layers of tantalum disulfide.
When two other amino acids were combined with tantalum disulfide, neither showed CCDW behavior at room temperature. The researchers found that the arginine molecule fits into the tantalum disulfide's crystal matrix like a puzzle piece. The perfect fit of the amino acid's size and how its electrons are distributed seem to explain its dramatic effect.
BACKGROUND
Normally, electrons move more or less randomly through a metal and are easily bumped off course by small-scale vibrations caused by ambient heat. The CCDW, based in the counterintuitive rules of the subatomic quantum world, exhibits orderly motion of electrons that instead flow with such distortions to a material's crystal structure. This special behavior could be harnessed in future technologies, but the need for extremely cold temperatures stands in the way.
METHOD
The researchers first put tantalum disulfide and arginine together in an earlier study that screened more than 50 different carbon-based molecules to see which ones combine with advanced materials. Extending the temperature range for the CCDW was a happy accident revealed in later analysis.
The current study compared the material to tantalum disulfide on its own, using a variety of techniques that measure vibrations, electrical flow, temperature changes and atomic structure. Computer simulations helped establish why arginine changed the quantum material's behavior.
IMPACT
The investigators' use of an amino acid is a rare example of inorganic materials chemists using molecular chemistry to modulate electronic behavior of inorganic crystals. The findings may open up the design space for advanced materials to include other molecules of life.
The researchers' next steps will seek to advance understanding of both the material and the method.
With further development, the tantalum disulfide-arginine combo could provide the basis for new technologies such as energy-efficient computer memory. That would be an entirely new type of storage based in quantum properties, instead of the electrons that are the basis for traditional electronics.
The happy accident spurring the study may lead to a new way to extend the capabilities of quantum materials. The specifications that made arginine such a perfect match for tantalum disulfide could one day inform rational design — starting with a desired property, such as superconductivity, and then identifying or designing molecules to achieve it.
AUTHORS
The study's corresponding author is Xiangfeng Duan, the holder of UCLA's Raymond A. and Dorothy A. Wilson Endowed Chair and a distinguished professor of chemistry and biochemistry. The co-first authors of the study are UCLA postdoctoral researchers Jingyuan Zhou and Boxuan Zhou. The research team led by USC engineering professor Zhenglu Li made important contributions to the study's theoretical analysis. Other co-authors are affiliated with UCLA, Tamkang University in Taiwan, UC Irvine and the University of Chemistry and Technology, Prague, in the Czech Republic.
JOURNAL
The study was published in Nature Chemistry.
FUNDING
The research was supported by the U.S. National Science Foundation; the U.S. Department of Energy; Taiwan's National Science and Technology Council; the Czech Republic's ERC-CZ program and Ministry of Education, Youth and Sports; the European Regional Development Fund; and the Elman Family Innovation Fund at CNSI.
