A fascinating new discovery has emerged from a team of scientists who have identified an unexpected way heat moves through a quantum material, shaking up our traditional views on thermal transport in semimetals. This groundbreaking research, spearheaded by experts from Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the University of Bonn, and the Centre national de la recherche scientifique (CNRS), shows that magnetic fields can actually trigger quantum oscillations in heat conduction, even in materials where we thought this kind of behavior was off the table.
Their findings, published in the journal Proceedings of the National Academy of Sciences (PNAS), highlight that the semimetal zirconium pentatelluride (ZrTe₅) displays remarkably strong thermal oscillations when subjected to extremely low temperatures and powerful magnetic fields. This revelation offers fresh insights into the dynamics of quantum heat.
ZrTe₅ is part of a unique group of materials known as topological semimetals, which are distinguished by their special electronic structures that allow for stable, topologically protected conduction. These materials are not just interesting for their unusual properties; they also hold great promise for future applications in quantum computing, high-precision electronics, and magnetic sensing technologies.
“Typically, metals like silver or copper show oscillations in thermal conductivity when exposed to strong magnetic fields close to absolute zero. This effect arises from the quantum behavior of electrons near the Fermi surface,” said Dr. Stanisław Gałeski, an assistant professor at Radboud University and a visiting scientist at the Dresden High Magnetic Field Laboratory (HLD) at HZDR. “However, in semimetals—where there are fewer charge carriers—thermal transport is usually thought to be governed by phonons, which are the quanta of lattice vibrations. Consequently, quantum oscillations in thermal conductivity have long been considered undetectable in these materials.”
The study reveals some fascinating insights about ZrTe₅, showing that while thermal transport is primarily driven by phonons, strong magnetic fields can really shake things up. When this material is exposed to such fields, the energies of electrons get locked into distinct quantum levels, which boosts the interactions between electrons and phonons. This leads to phonons starting to show off their quantum traits, including some interesting oscillatory behavior in thermal conduction.
Dr. Toni Helm from the HLD at HZDR commented, “This is a highly unconventional process. The phonons pick up quantum characteristics from the electrons due to the stronger coupling, and they start to display thermal quantum oscillations—a phenomenon that was once thought impossible in semimetals.”
By taking detailed measurements of thermal conductivity and ultrasonic attenuation in ZrTe₅ at temperatures just above absolute zero, the researchers were able to spot clear quantum oscillations that matched the frequency of the electronic system. Interestingly, the way the oscillation amplitude changed with temperature aligned with phonon characteristics, lending strong support to the proposed mechanism.
Looking at the Bigger Picture for Quantum Materials
What’s really exciting is that this mechanism isn’t just a one-off for ZrTe₅. The researchers believe it could apply to all semimetals with low charge-carrier densities, whether they’re topological or not. This includes well-known materials like graphene and bismuth, which opens up new possibilities for exploring subtle quantum phenomena through phonon-based methods.
The study emphasizes that thermal conductivity measurements—often seen as just engineering tools—can actually act as sensitive indicators of quantum behavior, providing insights into effects that might be tricky to catch using traditional electronic methods.
