Beating Carnot efficiency with periodically driven chiral conductors

Area of Science:

• Quantum thermodynamics
• Mesoscopic physics
• Condensed matter physics

Background:

• Classical thermodynamics dictates that ideal thermal machines are bound by the Carnot efficiency limit.
• The validity of this limit for microengines operating far from thermodynamic equilibrium remains an open question.
• Recent advancements focus on small conductors to explore the fundamental limits of thermodynamic engines.

Purpose of the Study:

• To investigate whether microengines operating far from equilibrium can exceed the Carnot efficiency limit.
• To analyze the thermodynamic performance of a quantum chiral conductor driven by AC voltage.
• To determine if the second law of thermodynamics is preserved under these conditions.

Main Methods:

• Theoretical analysis of a quantum chiral conductor subjected to an AC voltage.
• Investigation of photoassisted excitation processes and their role in entropy production.
• Examination of work extraction from temperature baths and its implications for thermodynamic laws.

Main Results:

• Demonstration that a quantum chiral conductor can achieve efficiencies significantly exceeding the Carnot bound.
• Observation of work extraction from temperature baths, seemingly violating the Kelvin-Planck statement.
• Confirmation that entropy production remains positive, preserving the second law of thermodynamics with a proper definition.

Conclusions:

• The study highlights that efficiencies beyond the Carnot limit are achievable in specific quantum systems.
• Key factors enabling超-Carnot efficiencies include irreversible entropy production via AC field-induced excitations and chirality-induced absence of power injection.
• These findings offer crucial insights into the fundamental limits of thermodynamic engines at the microscale.