Beating Carnot efficiency with periodically driven chiral conductors

TL;DR

This paper demonstrates that a quantum chiral conductor driven by AC voltage can surpass the Carnot efficiency limit, challenging classical thermodynamics while still respecting the second law through entropy considerations.

Contribution

It shows that chiral quantum conductors driven periodically can achieve efficiencies beyond Carnot by leveraging irreversibility and chirality, redefining thermodynamic bounds.

Findings

Efficiency exceeds Carnot limit in chiral conductors with AC driving

Entropy production remains positive, preserving the second law

Work can be extracted from common temperature baths, violating Kelvin-Planck

Abstract

Classically, the power generated by an ideal thermal machine cannot be larger than the Carnot limit. This profound result is rooted in the second law of thermodynamics. A hot question is whether this bound is still valid for microengines operating far from equilibrium. Here, we demonstrate that a quantum chiral conductor driven by AC voltage can indeed work with efficiencies much larger than the Carnot bound. The system also extracts work from common temperature baths, violating Kelvin-Planck statement. Nonetheless, with the proper definition, entropy production is always positive and the second law is preserved. The crucial ingredients to obtain efficiencies beyond the Carnot limit are: i) irreversible entropy production by the photoassisted excitation processes due to the AC field and ii) absence of power injection thanks to chirality. Our results are relevant in view of recent developments that use small conductors to test the fundamental limits of thermodynamic engines.