A quantum-dot heat engine operating close to the thermodynamic efficiency limits

• Published in: Nature nanotechnology Vol. 13; no. 10; pp. 920 - 924
• Main Authors: Josefsson, Martin, Svilans, Artis, Burke, Adam M., Hoffmann, Eric A., Fahlvik, Sofia, Thelander, Claes, Leijnse, Martin, Linke, Heiner
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-10-2018; Nature Publishing Group
• Subjects: 639/766/530/951; 639/925/927/1007; Chemistry and Materials Science; Condensed Matter Physics; Coolers; Den kondenserade materiens fysik; Efficiency; Electric power; Energiteknik; Energy conversion efficiency; Energy Engineering; Energy harvesting; Engineering and Technology; Filtration; Fysik; Harvesters; Heat; Heat engines; Heat exchange; Heat flow; Heat transmission; Letter; Maskinteknik; Materials Science; Maximum power; Mechanical Engineering; Miniaturization; Nanotechnology; Nanotechnology and Microengineering; Nanowires; Natural Sciences; Naturvetenskap; Photovoltaics; Physical Sciences; Power efficiency; Predictions; Quantum dots; Teknik; Thermodynamic efficiency
• ISSN: 1748-3387; 1748-3395
• DOI: 10.1038/s41565-018-0200-5

Cyclical heat engines are a paradigm of classical thermodynamics, but are impractical for miniaturization because they rely on moving parts. A more recent concept is particle-exchange (PE) heat engines, which uses energy filtering to control a thermally driven particle flow between two heat reservoirs
1
,
2
. As they do not require moving parts and can be realized in solid-state materials, they are suitable for low-power applications and miniaturization. It was predicted that PE engines could reach the same thermodynamically ideal efficiency limits as those accessible to cyclical engines
3
–
6
, but this prediction has not been verified experimentally. Here, we demonstrate a PE heat engine based on a quantum dot (QD) embedded into a semiconductor nanowire. We directly measure the engine’s steady-state electric power output and combine it with the calculated electronic heat flow to determine the electronic efficiency
η
. We find that at the maximum power conditions,
η
is in agreement with the Curzon–Ahlborn efficiency
6
–
9
and that the overall maximum
η
is in excess of 70% of the Carnot efficiency while maintaining a finite power output. Our results demonstrate that thermoelectric power conversion can, in principle, be achieved close to the thermodynamic limits, with direct relevance for future hot-carrier photovoltaics
10
, on-chip coolers or energy harvesters for quantum technologies.
Direct thermal-to-electric energy conversion can be performed at electronic efficiencies comparable to efficiencies of traditional cyclical heat engines.