Carnot cycle

Physics

Nanotechnology

Thermodynamic cycle

Organic chemistry

Energy conversion efficiency

Combustion

Maximum power principle

Power (physics)

Chemistry

Materials science

Thermodynamic temperature

Quantum thermodynamics

Brayton cycle

Miniaturization

Quantum mechanics

Thermal efficiency

Heat engine

Thermoelectric effect

Quantum

Thermodynamics

Nature Nanotechnology

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 reservoirs1,2. 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 engines3–6, 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 efficiency6–9 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 photovoltaics10, 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.

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