title: Collective couplings: Rectification and supertransmittance.
abstract: We investigate heat transport between two thermal reservoirs that are coupled via a large spin composed of N identical two-level systems. One coupling implements the dissipative Dicke superradiance. The other coupling is locally of the pure-dephasing type and requires to go beyond the standard weak-coupling limit by employing a Bogoliubov mapping in the corresponding reservoir. After the mapping, the large spin is coupled to a collective mode with the original pure-dephasing interaction, but the collective mode is dissipatively coupled to the residual oscillators. Treating the large spin and the collective mode as the system, a standard master equation approach is now able to capture the energy transfer between the two reservoirs. Assuming fast relaxation of the collective mode, we derive a coarse-grained rate equation for the large spin only and discuss how the original Dicke superradiance is affected by the presence of the additional reservoir. Our main finding is a cooperatively enhanced rectification effect due to the interplay of supertransmittant heat currents (scaling quadratically with N) and the asymmetric coupling to both reservoirs. For large N, the system can thus significantly amplify current asymmetries under bias reversal, functioning as a heat diode. We also briefly discuss the case when the couplings of the collective spin are locally dissipative, showing that the heat-diode effect is still present.
authors.affiliation: Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstraße 36, D-10623 Berlin, Germany.
authors.forename: Gernot
authors.initials: G
authors.lastname: Schaller
authors.affiliation: Mathematical Soft Matter Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna, Okinawa 904-0495, Japan.|Dipartimento di Matematica e Fisica and ILAMP, Università Cattolica del Sacro Cuore, I-25121 Brescia, Italy.|Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, via Bassi 6, I-27100 Pavia, Italy.
authors.forename: Giulio Giuseppe
authors.initials: GG
authors.lastname: Giusteri
authors.affiliation: Dipartimento di Matematica e Fisica and ILAMP, Università Cattolica del Sacro Cuore, I-25121 Brescia, Italy.|Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, via Bassi 6, I-27100 Pavia, Italy.|Instituto de Física, Benemérita Universidad Autónoma de Puebla, Apartado Postal J-48, Puebla 72570, Mexico.
authors.forename: Giuseppe Luca
authors.initials: GL
authors.lastname: Celardo