An Amino Acid Keeps a Quantum Electron Pattern Alive 150 Degrees Celsius Warmer

A building block of proteins has pushed a delicate quantum state of matter from deep-freeze territory to well above room temperature, according to a study from a UCLA-led team published in Nature Chemistry.

The research began with a material that behaves unusually when extremely cold: 135 degrees below zero Fahrenheit (minus 93 Celsius), close to the lowest temperature ever recorded in Antarctica. The team showed that the behavior could be extended to about 135 F (57 C), close to the highest heat ever measured in Death Valley. That is a gain of roughly 150 degrees Celsius, or 270 degrees Fahrenheit.

The base material was a stack of sheets only three atoms thick, made from a compound called tantalum disulfide. Its special behavior is known as the commensurate charge density wave, or CCDW. In an ordinary metal, electrons move more or less randomly and are easily knocked off course by small vibrations caused by ambient heat. In a CCDW, the electrons instead move together in a pattern that traces the internal structure of the crystal. The behavior comes from the counterintuitive rules of the quantum world, and it could be useful in future technology, but the need for extreme cold has stood in the way.

The key step was a surprise: adding an amino acid called arginine. The combined material is built from repeated vertical stacks, with two layers of arginine sandwiched between single layers of tantalum disulfide. When the team tried two other amino acids with tantalum disulfide, neither showed CCDW behavior at room temperature. Arginine, the researchers found, fits into the crystal matrix like a puzzle piece. The match between the molecule's size and how its electrons are distributed appears to explain its dramatic effect.

The result was partly luck. The team had first combined tantalum disulfide and arginine in an earlier study that screened more than 50 carbon-based molecules to see which ones pair with advanced materials. The wider temperature range showed up only in later analysis, which the researchers called a happy accident. For the current study they compared the combined material with tantalum disulfide on its own using techniques that measure vibrations, electrical flow, temperature changes and atomic structure. Computer simulations helped establish why arginine changed the behavior.

The work was an international collaboration led by investigators at the UCLA College and the California NanoSystems Institute at UCLA. The researchers describe the use of an amino acid as a rare example of inorganic materials chemists using molecular chemistry to tune the electronic behavior of inorganic crystals. They say the findings may widen the design space for advanced materials to include other molecules of life.

The team's next steps are to deepen understanding of both the material and the method. With further development, they say, the tantalum disulfide and arginine combination could underpin technologies such as energy-efficient computer memory, a new type of storage based on quantum properties rather than the electrons used in conventional electronics. The specifications that made arginine such a good match could also guide rational design, starting from a desired property such as superconductivity and then identifying or designing molecules to achieve it.