Traditionally, most thermoelectric devices leverage the longitudinal thermoelectric effect, where electric current flows in the same direction as heat movement. These devices are typically constructed from alternating layers of p-type and n-type semiconductors arranged in series. This design exploits the opposing charge carrier motions in response to temperature gradients. However, the complexity of this multi-layer design introduces significant challenges, notably increased electrical contact resistance, which can lead to energy losses and restrict the system’s efficiency.

Recent advancements have directed attention toward transverse thermoelectric (TTE) devices, which promise a more efficient alternative. Unlike traditional designs, TTE devices function by generating a voltage perpendicular to the direction of heat flow. This fundamental shift allows for the use of a single type of material, thus eliminating the need for multiple interfaces. The reduction in contact resistance not only simplifies manufacturing processes but has also been shown to enhance device performance significantly, although suitable materials exhibiting strong TTE effects remain scarce.

A groundbreaking study conducted by a research team, spearheaded by Associate Professor Ryuji Okazaki from the Tokyo University of Science, recently delineated the potential of molybdenum disilicide (MoSi2) to inspire the next generation of TTE materials. This mixed-dimensional semimetal displayed significant transverse thermoelectric behavior. With collaborative contributions from several researchers within the team, their findings illuminate an entirely new direction in material design and identification for TTE applications.

The research focused heavily on the unique transport properties of MoSi2, utilizing a combination of experimental measurements and first-principles calculations to gauge various physical properties, including resistivity, thermal conductivity, and longitudinal thermopower. A key focus was placed on assessing how these properties varied along the material’s two crystallographic axes. The results highlighted a pronounced axis-dependent conduction polarity (ADCP), a notable feature that was corroborated through Hall resistivity investigations.

Delving deeper into the origins of this ADCP, the team utilized advanced computational methods to analyze the electronic structure of MoSi2. One pivotal finding was the material’s mixed-dimensional Fermi surface structure, characterized by the existence of two Fermi surfaces with opposing polarities. Such structural nuances are crucial, as they dictate many of the electronic and transport characteristics fundamental to the material’s thermoelectric behavior.

Through meticulous experimentation, the researchers advanced their investigation by applying a temperature difference at a 45-degree angle to one of the crystallographic axes of MoSi2. This innovative approach yielded remarkably clear transverse thermopower signals, thereby validating the material’s applicability for TTE devices. Notably, the magnitude of the thermopower observed in MoSi2 outpaced that seen in other candidate materials, including tungsten disilicide (WSi2), credited primarily to the distinct electron distribution patterns inherent to MoSi2.

The implications of these findings extend beyond fundamental research; they signal a potential revolution in the development of efficient heat recovery systems. By implementing thin films of MoSi2 within TTE applications, researchers foresee the possibility of harnessing larger heat source areas, which could dramatically enhance voltage production capabilities. Furthermore, the efficiency gains offered by MoSi2 may facilitate the transition towards low-temperature applications, broadening the scope of viable materials in this emerging field.

Professor Okazaki’s observations bring to light the significance of mixed-dimensional Fermi surfaces as a critical variable influencing ADCP and, correspondingly, the efficacy of transverse thermopower generation. This insight solidifies MoSi2’s status as a frontrunner in TTE research, setting a precedent for subsequent investigations aimed at exploring and exploiting similarly structured materials.

The study ultimately signifies not merely a step forward in material science but an essential pivot towards sustainable energy solutions. The potential applications of TTE devices utilizing MoSi2 can extend to various sectors, including electronic engineering and renewable energy, underscoring the pressing need to address energy loss mechanisms in traditional systems. As industries continue to seek pathways to reduce their carbon footprints, innovations such as those borne out of this research can play an integral role in shaping a greener, more sustainable future.

With this new understanding of MoSi2 and its capabilities, the research team is laying the groundwork for future exploratory efforts to discover and characterize additional materials that could further enhance thermoelectric device performance. As thermoelectric technologies gain traction, the prospect of efficient waste heat recovery systems becomes increasingly tangible, representing a blend of innovation and practicality that can lead us towards a more energy-conscious society.

In summation, the advancements in transverse thermoelectric materials illuminated by the Tokyo University of Science team’s research herald significant progress in thermoelectric technology. As researchers continue to uncover the complexities of materials like MoSi2, the possibilities for applying these solutions in real-world applications expand, demonstrating the vital interplay between material science and environmental sustainability in addressing global energy challenges.

Subject of Research: Transverse thermoelectric properties of MoSi2
Article Title: Axis-Dependent Conduction Polarity and Transverse Thermoelectric Conversion in the Mixed-dimensional Semimetal MoSi2
News Publication Date: 29-Dec-2025
Web References: DOI Link
References: None available
Image Credits: Associate Professor Ryuji Okazaki from Tokyo University of Science, Japan.

Keywords

The Thomson effect, first discovered by the eminent physicist William Thomson (later Lord Kelvin), is traditionally known as a fundamental thermoelectric effect, alongside the more widely recognized Seebeck and Peltier effects. These classical longitudinal thermoelectric effects involve the interplay of heat and charge currents moving parallel to one another within conductive materials. Historically, these effects have underpinned much of thermoelectric device engineering, focusing on harnessing temperature gradients to generate power or remove heat effectively through electrically driven processes.

In contrast, transverse thermoelectric phenomena involve interactions where heat and electric currents flow perpendicular to each other, leading to distinct effects such as the Nernst and Ettingshausen effects. These transverse effects, while known since the nineteenth century, have garnered increased scientific attention recently due to their simpler mechanical architectures and promising applications in advanced thermal management systems. Despite the theoretical anticipation of a transverse analog to the Thomson effect based on these underlying phenomena, direct experimental evidence remained lacking—until this landmark study.

The research team strategically utilized bismuth–antimony alloy samples, well-known for their pronounced thermoelectric characteristics, to probe the interplay of heat current, charge current, and magnetic field applied perpendicularly. Precise instrumentation enabled them to detect subtle heat release and absorption signals that deviated starkly from established thermoelectric signatures. Most notably, when the direction of the magnetic field was inverted, the observed heat release switched to heat absorption, incontrovertibly confirming the presence of a transverse Thomson effect.

This phenomenon is fundamentally different from the classical Thomson effect since it arises exclusively from the combined and simultaneous action of the Nernst and Ettingshausen effects—two well-characterized transverse thermoelectric processes. The Nernst effect describes the generation of a transverse electric field in response to a temperature gradient in a magnetic field, while the Ettingshausen effect refers to the creation of a transverse temperature gradient generated by an electric current in the presence of a magnetic field. The intricate synergy of these two effects culminates in the transverse Thomson effect, dictated by orthogonal vectors of heat, charge, and magnetic flux.

Methodologically, the experimental realization required unprecedentedly sensitive thermal measurements and meticulous control of all physical parameters to disentangle the transverse Thomson contribution from competing thermoelectric phenomena. The observed temperature modulations matched well with refined theoretical models, reinforcing confidence in the interpretation. This validation not only confirms a nearly two-century-old theoretical prediction but also expands the taxonomy of thermoelectric effects by adding a transverse counterpart to the Thomson effect.

Looking ahead, this pioneering observation paves the way for innovative thermal technologies that leverage magnetic fields to actively and reversibly manipulate heat flow at microscopic and macroscopic scales. Materials exhibiting stronger transverse Thomson coefficients could be tailored for devices capable of controlled heat release and absorption simply by switching the magnetic field’s polarity. Such capabilities could revolutionize cooling strategies in electronics, precision thermal regulation in sensors, and potentially impact energy conversion methods, enabling more compact, efficient, and versatile thermal management systems.

This discovery is a testament to the relentless progress in material physics and engineering, illustrating how classical concepts can find fresh relevance through contemporary experimental ingenuity. It bridges a critical gap between longstanding theoretical predictions and practical demonstration, enriching our fundamental understanding of thermoelectric phenomena. Moreover, it invites further investigation into the transverse Thomson effect across diverse materials and conditions, potentially uncovering new physics underlying coupled heat, charge, and magnetic interactions.

Beyond fundamental science, the ramifications of this work could extend into applied domains such as spintronics and magnonics, where heat and magnetism intertwine closely. The transverse Thomson effect adds a new dimension to this interplay, offering alternative mechanisms for thermal control and energy harvesting in next-generation functional materials. As researchers dive deeper into that rich parameter space, enhanced theoretical frameworks and sophisticated experimental setups will be crucial to unravel the full potential of transverse thermoelectric effects in practical contexts.

The collaborative nature of this achievement, integrating expertise across institutions and disciplines, highlights the importance of interdisciplinary approaches in uncovering subtle physical effects. Graduate student Atsushi Takahagi, alongside senior researchers Ken-ichi Uchida, Takamasa Hirai, Sang Jun Park, Hosei Nagano, and Abdulkareem Alasli, synthesized their respective specialties in materials science, mechanical engineering, and magnetism to realize this exceptional breakthrough. Their findings were published in the prestigious journal Nature Physics on June 26, 2025, marking a new chapter in thermoelectric research.

The study was supported by significant funding from the JST ERATO UCHIDA Magnetic Thermal Management Materials Project, JSPS Grants-in-Aid for Scientific Research, and fellowships, underscoring the critical investment in foundational materials science. This research not only validates long-discussed theoretical predictions but also galvanizes future explorations aimed at discovering and engineering materials with enhanced transverse thermoelectric responses.

In summary, the experimental observation of the transverse Thomson effect signifies a profound leap forward in the understanding and application of thermoelectric phenomena. By demonstrating the intricate coupling of heat, charge, and magnetic fields under orthogonal configurations, this work unlocks new realms of thermal control, offering exciting prospects for future materials innovation and device miniaturization. The ability to reversibly switch heat release and absorption by magnetic field manipulation brings us closer to sophisticated, actively tunable thermal devices that could transform numerous technological landscapes.

Subject of Research: Not applicable

Article Title: Observation of the transverse Thomson effect

News Publication Date: 26-Jun-2025

Web References: http://dx.doi.org/10.1038/s41567-025-02936-3

Image Credits: Ken-ichi Uchida, National Institute for Materials Science; Hosei Nagano, Nagoya University

Keywords

Transverse Thomson effect, thermoelectric phenomena, Nernst effect, Ettingshausen effect, thermal management, magnetic field, bismuth–antimony alloys, heat current, charge current, thermodynamics, energy conversion, materials science