Heat flow in nonlinear molecular junctions: Master equation analysis

Abstract

We investigate the heat conduction properties of molecular junctions comprising anharmonic interactions. We find that nonlinear interactions can lead to novel phenomena: negative differential thermal conductance and heat rectification. Based on analytically solvable models we derive an expression for the heat current that clearly reflects the interplay between anharmonic interactions, strengths of coupling to the thermal reservoirs, and junction asymmetry. This expression indicates that negative differential thermal conductance shows up when the molecule is strongly coupled to the thermal baths, even in the absence of internal molecular nonlinearities. In contrast, diode like behavior is expected for a highly anharmonic molecule with an inherent structural asymmetry.Anharmonic interactions are also necessary for manifesting Fourier type transport. We briefly present an extension of our model system that can lead to this behavior.

Two-level system in spin baths: Non-adiabatic dynamics and heat transport

“…We have recently extended the NIBA to the out-of-equilibrium two-bath case, considering harmonic environments of different temperatures [19,20,25]. Next we further point out that this extension holds for spin environments.…”

“…Given the complex dissipative dynamics observed in the single-bath model, it is not surprising that the related out-of-equilibrium version exhibits a rich transport behavior [21][22][23][24]. We have recently extended the non-interacting blip approximation [4,8,9] and studied heat transport characteristics in the two-bath spin-boson model in the non-adiabatic regime [19,20,25]: We have validated the heat exchange fluctuation theorem in this many-body model and demonstrated that the heat current can display a significant negative differential thermal conductance (NDTC). To understand heat transport in actual nanostructures, it is of interest to explore transport behavior between other reservoirs, particularly considering anharmonic environments.…”

“…The simple picture can be extended to the out-of-equilibrium regime by coupling the central spin to two separate (spatially or energetically) thermal reservoirs which are maintained at different temperatures. This setup has been proposed as a toy model for exploring quantum transport phenomenology in an anharmonic nanojunction [19,20]. Given the complex dissipative dynamics observed in the single-bath model, it is not surprising that the related out-of-equilibrium version exhibits a rich transport behavior [21][22][23][24].…”

Effects of vibrational anharmonicity on molecular electronic conduction and thermoelectric efficiency

“…Finally, the QME as described here can be used to examine a range of transport problems, by turning on/off different reservoirs. Besides the analysis of inelastic electronic conduction with anharmonic modes, one can use this method and study the operation of phononthermoelectric transistors 53 and phononic thermal junctions with harmonic and anharmonic local modes, to demonstrate nonlinear function such as thermal rectification and negative differential thermal conductance 62 . To derive Eq.…”

Theory of quantum energy transfer in spin chains: Superexchange and ballistic motion

“…Under these conditions baths' modes in resonance with the subsystem frequencies are populated, responsible for the subsystem excitation and relaxation processes. This resonance energy transfer process can be treated within the BornMarkov approximation scheme [42,43]. In Sec.…”