Figure 1: A crystal of tellurium that RIKEN researchers grew and then used to observe a nonlinear thermoelectric effect. © 2026 RIKEN Center for Emergent Matter Science
An unusual thermoelectric effect has been observed in the semiconductor tellurium by RIKEN physicists for the first time1. This demonstration points to the potential of similar materials to be used in applications such as energy harvesting and advanced heat management.
Thermoelectric materials can convert electricity into heat and vice versa. For most of them, doubling the voltage across them will double the heat they produce. But for some special thermoelectric materials, there is a nonlinear relationship between voltage and heat. Such nonlinear thermoelectric materials are useful for applications that require heat to flow in one direction and for generating electricity from thermal fluctuations.
Some theoretical calculations have predicted that even more exotic nonlinear thermoelectric effects will occur in materials where the atoms or molecules have a chiral arrangement. But they hadn't been observed in the lab-until now.
Tetsuya Nomoto, Fumitaka Kagawa and their co-workers, all at the RIKEN Center for Emergent Matter Science, have now experimentally confirmed these theoretical predictions.
Specifically, they showed that creating a temperature difference across the semiconductor tellurium and applying an electric field at right angles to it generates a voltage in the third perpendicular direction. It's an exotic variation of the Hall effect, in which a current flowing through a conductor veers to the right when a magnetic field is applied at right angles to the current.
This effect could be used for research applications. "We expect it to be useful at the laboratory level as a probe for investigating quantum geometric properties within materials or as a means for determining material chirality," says Nomoto.
The team's experience in performing high-precision measurements allowed them to pull off this highly demanding observation.
"We've worked on heat transport and thermoelectric phenomena in quantum materials for many years, along with developing high-precision measurement systems," says Nomoto. "Building on that foundation, we designed and built a new experimental setup and used it to observe a theoretically proposed nonlinear thermoelectric response."
The team was surprised at how large the effect was-of the order of microvolts. "We initially expected the signal to be extremely small," recalls Nomoto. "In the experiments, however, we found a comparatively large signal, and its magnitude was surprisingly consistent with recent theoretical predictions."
Nomoto and team now intend to conduct follow-up studies to explore the effect further. "Many aspects of the nonlinear chiral thermoelectric effect remain unclear-for example, its detailed temperature dependence and the underlying microscopic mechanisms," says Nomoto. "We therefore plan to deepen our understanding of this phenomenon, including by extending measurements to chiral materials beyond tellurium."
Kazuki Nakazawa (left), Tetsuya Nomoto (middle), Fumitaka Kagawa (right) and co-workers have observed the nonlinear chiral thermoelectric Hall effect in the semiconductor tellurium. © 2026 RIKEN
