New Kondo Semimetal Discovered with quantum criticality

Credit: TU Wien

Quantum properties are studied by phase transitions which occur at absolute zero points of temperature. These transitions depend on parameters such as a magnetic field and are called Quantum Phase Transitions or Quantum Critical Points.

A team of researchers has found these quantum critical points in a novel material, and the properties of this material are now being further investigated due to its pristine form and behavior. The material is suspected to be a Weyl-Kondo semimetal, which is a very special material due to its special quantum states, and could be a key for the development of topological quantum materials.

This study was published in the journal, Science Advances. The results were found by TU Wien, Johns Hopkins University, the National Institute of Standards and Technology, and Rice University.

The material is a compound of Cerium, Ruthenium, and Tin (CeRu₄Sn₆). The thing is that quantum critical behavior is studied in metals or insulators, but this is a semimetal, with properties that lie between metals and semiconductors. “Usually, quantum criticality can only be created under particular 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.” said, Wesely Fuhrman, a Ph.D. student at Johns Hopkins University, “Normally, you have to work hard to produce the appropriate laboratory conditions, but this semimetal provides the quantum criticality all by itself.”

This behavior is related to the behavior of electrons in this material, it is a highly correlated electron system, which makes electron interact with each other very strongly, the interaction leads to a Kondo effect, where a quantum spin in the material is shielded by electrons surrounding it, so the spin no longer has any effects on the material. If there are only relatively few free electrons, like in a semimetal, then the Kondo effect is unstable, which could be the reason for the quantum critical behavior of the material, as the system fluctuates between a state with and a state without Kondo effect, which has the effect of a phase transition at absolute zero temperature.

Weyl fermions occur in solids in form of quasiparticles, as collective excitations such as waves in a pond, and according to the predictions, such Weyl fermions should exist in this material theoretically, so, therefore, quantum critical fluctuations could stabilize Weyl fermions like in a similar way to critical quantum fluctuations in high-temperature superconductors holding superconducting Cooper pairs together. 

This material, if it turns out to be Weyl-kondo semimetal then that could be used in many applications, as the topological states are very stable and are unlike to be disturbed by external forces, which makes them interesting for quantum computers. 

Bühler-Paschen said, “This could lead to the establishment of a design concept with which such materials can be specifically improved, tailored, and used for concrete applications.”

For further results, measurements under different external conditions are to be carried out.

Refernce: DOI: 10.1126/sciadv.abf9134