New Quantum Material Discovery

By Scott Hamilton

Senior Expert Emerging Technologies 

A research team from TU Wein, in partnership with several U.S. research institutes, discovered a unique material that could prove useful in quantum technologies. The new material that consists of a combination of ruthenium, cerium and tin has a unique property. The material goes through quantum phase transitions when exposed to magnetic fields.

I guess before you can understand the importance of such a discovery, you need to understand exactly what a quantum phase transition is. You experience phase transitions everyday as the ice melts in your drink. We are all familiar with phase transitions like the ones associated with temperature changes. Ice becomes water and eventually steam as the temperature rises. Some of you may remember experiments from high school science where you lowered the air pressure in a container and watched cold water boil. This proved that phase changes can occur with other external influences. Water can transition to steam with both a change in pressure or a change in temperature.

There are other types of phase transitions that occur at the subatomic level; these are quantum phase transitions. The most interesting quantum phase transitions are those that occur at near absolute zero temperatures by exposure to things like radiation, light and magnetism. These transitions are used to create quantum computers through the ability to control the phase shifts from external influences. The problem is that many materials have multiple triggers for the phase transitions, like light, radiation, vibration, magnetism and temperature. This makes it difficult to control the quantum states.

The new material discovered by the Austrian-American research team was in a fairly novel material that was not in a pristine form, which makes the discovery even more exciting. They can see the property in poorly processed samples, which means it is easy to create this quantum material. Materials that have easily manipulated quantum states by magnetic fields fall in a class of materials known as Weyl-Kondo semimetals. These materials have been discovered in the past but the properties were only seen in very pristine samples. The discovery in relatively raw materials was a major breakthrough.

Microsoft has been working on what they term topological quantum processors for a number of years, but has been struggling to find a material that would allow them to control the quantum states in a topological manner. This new material seems to exhibit those properties, and if this proves to be true, the missing link to topological quantum processors has been found.

The initial results were found in cooperation with researchers from TU Wien, Johns Hopkins University, the National Institute of Standards and Technology (NIST) and Rice University, and were recently published in the journal “Science Advances.”

“Usually quantum critical behavior is studied in metals or insulators. But we have now looked at a semimetal,” says Prof. Silke Bühler-Paschen from the Institute of Solid State Physics at TU Wien. The material is a compound of cerium, ruthenium, and tin — with properties that lie between those of metals and semiconductors.

Usually, quantum criticality can only be created under very specific environmental conditions — a certain pressure or an electromagnetic field. “Surprisingly, however, our semimetal turned out to be quantum critical without any external influences at all,” says Wesley Fuhrman, a PhD student in Prof. Collin Broholm’s team at Johns Hopkins University, who made an important contribution to the result with neutron scattering measurements. “Normally you have to work hard to produce the appropriate laboratory conditions, but this semimetal provides the quantum criticality all by itself.”

Until next week stay safe and learn something new. 

Scott Hamilton is a Senior Expert in Emerging Technologies at ATOS and can be reached with questions and comments via email to sc************@at**.net or through his website at https://www.techshepherd.org.