Inverse Current in Coupled Transport: A Quantum Thermodynamic Framework for Energy and Spin-polarized Particle Currents

Abstract: The phenomenon of inverse current in coupled transport (ICC), where one induced current flows counter to two parallel thermodynamic forces, represents a strikingly counterintuitive behavior in transport processes [Phys. Rev. Lett. 124, 11607 (2020)]. Through an exactly solvable model of strongly coupled quantum dots, we provide a quantum thermodynamic framework to describe ICC in energy and spin-polarized particle currents, highlighting its potential applications for unconventional and autonomous nanoscale thermoelectric engines and refrigerators. Our analysis establishes a link between the microscopic and macroscopic descriptions of the entropy production rate, emphasizing the crucial role of thermodynamic forces and their conjugate fluxes in accurately characterizing genuine ICC. Here, the paradoxical behavior of ICC emerges from the symmetry breaking between particle and energy transitions, identified as the sufficient condition, while the attractive interaction between the coupled quantum dots is determined to be the necessary criterion for the ICC effect.