Abstract: Transverse Thomson effect

The thermoelectric effects have attracted attention as principles for energy harvesting and thermal management technologies. The Seebeck, Peltier, and Thomson effects, categorized as longitudinal thermoelectric effects, were discovered in 19th century and have been systematically studied for a long time. The Thomson effect generates volumetric heating or cooling in a conductor when a charge current and temperature gradient are applied in the same direction. The heat source of the Thomson effect is determined solely by the temperature derivative of the Seebeck coefficient; this is known as the first Thomson (Kelvin) relation. On the other hand, the transverse thermoelectric effects including the Nernst and Ettingshausen effects were discovered in the same century, but the transverse Thomson effect (TTE) has only been predicted theoretically and has not yet been observed experimentally [1]. According to the analogy with the Thomson effect, TTE should be related to the temperature derivative of the Nernst coefficient. The observation of TTE is an important task for systemizing the transverse thermoelectric effects.

In this study, we directly observed the thermal response of TTE by applying a charge current, temperature gradient, and magnetic field in the orthogonal directions to a nonmagnetic conductor, using thermoelectric imaging based on the lock-in thermography method [2]. We measured the dependence of TTE on the charge current, temperature gradient, and magnetic field systematically and performed numerical simulations for TTE based on the thermoelectric transport model. Our experimental and numerical results clarified that TTE is determined not only by the temperature derivative of the Nernst coefficient but also the Nernst coefficient itself, which essentially differs from the conventional Thomson effect. Thus, materials with the large Nernst coefficient could be promising candidates for realizing large TTE. This result fills a missing piece in thermoelectrics and spin caloritronics, and further unobserved phenomena such as anomalous TTE are expected to be demonstrated in the future.

References:

[1] L. D. Landau, E. M. Lifshitz, and L. P. Pitaevskii, Electrodynamics of Continuous Media (Pergamon Press, Oxford, 1984).

[2] A. Takahagi, et al. Nat. Phys. (2025). https://doi.org/10.1038/s41567-025-02936-3