Quantum heat transport in a spin-boson nanojunction: Coherent and incoherent mechanisms

Abstract

Quantum heat transport in a spin-boson system under nonequilibrium steady state (NESS) is investigated by the nonequilibrium Green's function (NEGF) method. Spin-spin correlators are calculated via the Majorana fermion representation of spin operators, which allows us to make use of Wick's theorem through standard diagrammatic techniques. An analytic formula of heat current is obtained, and numerical results are presented in comparison with those obtained by other methods. Two types of transport mechanisms are identified in high-and low-temperature regions, respectively, which shows a transition from incoherent to coherent transport process with the baths' temperatures decreased. Additionally, a saturation of the heat current is confirmed when increasing the coupling strength between the baths and the intermediate system, which is a sign of quantum Zeno effect (QZE) in the transport process.

Energy transfer in the nonequilibrium spin-boson model: From weak to strong coupling

“…which is exactly the result obtained by a previous NEGF method [15]. When the bath temperature T L/R is comparable to or larger than the energy spacing ∆ of the spin, the incoherent sequential process becomes the dominant heat transfer mechanism [11], thus the integrand of Eq.…”

“…Therefore, in terms of Keldysh GFs defined above, a formal expression for the energy current from vth bosonic bath to the system can be expressed as [15,26,36] …”

“…We note that a combination of the MFDM and the NEGF leads to conservation laws and can also be applied to a wide range of temperature in the weak coupling regime [15,29]. Thus we follow this framework and absorb these advantages into our theory.…”

Energy current and its statistics in the nonequilibrium spin-boson model: Majorana fermion representation

“…Among the techniques developed to study the characteristics of the thermal heat current in the NESB model we recount perturbative quantum master equation tools: Redfield equation [5-7, 9, 25], the noninteracting blip approximation (NIBA) [6,7,26], as well as Keldysh nonequilibrium Greenʼs function (NEGF) methods [27,28]. Furthermore, efforts have been made to go beyond the standard Born-Markov limit, and include higher order co-tunneling processes [29].…”

“…A theory interpolating these two limits was presented in [30]. However, these studies still miss the low temperature limit [28].…”