Institute of Science Tokyo and collaborators develop technology for highly efficient thermoelectric conversion of waste heat from electronic devices

A research group led by Professor Toshimasa Fujisawa from the Department of Physics, School of Science at the Institute of Science Tokyo and Senior Distinguished Researcher Koji Muraki from the Basic Research Laboratories, NTT Inc. announced on October 1 that they have developed an energy harvesting technology that enables thermal efficiency exceeding thermodynamic efficiency limits by utilizing non-thermal states that exist stably in interacting one-dimensional electron systems called "Tomonaga-Luttinger liquids." The experiment confirmed that waste heat from electronic devices can be channeled into this liquid and transported to a distant heat engine where the heat can be extracted, without reaching thermal equilibrium. This is expected to contribute to reducing environmental impact. The results were published in Communications Physics on September 30.

Interest in energy harvesting technology that converts waste heat into electricity is growing. Conventional energy harvesting technologies are premised on thermoelectric conversion from waste heat that has reached thermal equilibrium and have been constrained by thermodynamic efficiency limits such as Carnot efficiency (the maximum thermal efficiency obtained by reducing the extracted power to zero at the limit) and Curzon-Ahlborn efficiency (the thermal efficiency under conditions that maximize the extracted power).

While there are reports of heat engines that exceed this upper limit by utilizing non-thermal states different from thermal equilibrium, many non-thermal states are special states created artificially. Applying them as-is to energy harvesting technologies has been difficult.

In this research, the group focused on the fact that by using Tomonaga-Luttinger liquids as a medium for heat transport, non-thermal states can be easily created, and heat can be transported while maintaining those non-thermal states.

Tomonaga-Luttinger liquids are collections of one-dimensional electrons in which electrons interact strongly with each other, exhibiting wave-like properties as a collective, where non-thermal states can exist stably.

In the experiment, the researchers succeeded in channeling waste heat from a transistor into the Tomonaga-Luttinger liquid, transporting the non-thermal state generated to a heat engine using quantum dots, and extracting electrons.

The thermoelectric properties, including thermal efficiency, were evaluated based on the conditions of the quantum dots under which electrons can be extracted.

As a result, it was confirmed that when compared with quasi-thermalized states, using non-thermal states enables higher electromotive force (voltage) to be obtained, higher maximum thermal efficiency, and thermoelectric conversion with high thermal efficiency even at maximum power output.

It was found that high thermal efficiency exceeding thermodynamic efficiency limits such as Carnot efficiency and Curzon-Ahlborn efficiency can be obtained.

Fujisawa commented: "I believe that the fascination of condensed matter physics research lies in the ability to contribute to the development of society by discovering interesting properties and manifesting new functionalities. This work demonstrates that high thermoelectric conversion efficiency can be achieved through research on the properties of one-dimensional electron systems. Although the power generated is still minimal, I think applications to energy reuse in electronic devices will become possible by pursuing higher power generation."

Journal Information
Publication: Communications Physics
Title: Efficient heat-energy conversion from a non-thermal Tomonaga-Luttinger liquid
DOI: 10.1038/s42005-025-02297-6