A Self Energy Model of Dephasing in Molecular Junctions

Penazzi, Gabriele; Pecchia, Alessandro; Frauenheim, Thomas

doi:10.1021/acs.jpcc.6b04185

Cited by 12 publications

(14 citation statements)

References 56 publications

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“…As we demonstrate in the SI, qualitatively similar behaviour can be obtained when modelling the environmental interactions using a dephasing approach within the non-equilibrium Green function formalism. [31][32][33] In practical realisations of single-molecule thermoelectric materials one should, therefore, strive to minimise the environmental vibrational coupling. Examples of systems attractive in this context (i.e.…”

Section: Devicesmentioning

confidence: 99%

Marcus Theory of Thermoelectricity in Molecular Junctions

2019

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Thermoelectric energy conversion is perhaps the most promising of the potential applications of molecular electronics. Ultimately, it is desirable for this technology to operate at around room temperature, and it is therefore important to consider the role of dissipative effects in these conditions. Here, we develop a theory of thermoelectricity which accounts for the vibrational coupling within the framework of Marcus theory.We demonstrate that the inclusion of lifetime broadening is necessary in the theoretical description of this phenomenon. We further show that the Seebeck coefficient and the power factor decrease with increasing reorganisation energy, and identify the optimal operating conditions in the case of non-zero reorganisation energy. Finally, with the aid of DFT calculations, we consider a prototypical fullerene-based molecular junction.We estimate the maximum power factor that can be obtained in this system, and confirm that C 60 is an excellent candidate for thermoelectric heat-to-energy conversion.This work provides general guidance that should be followed in order to achieve highefficiency molecular thermoelectric materials.The field of single-molecule electronics, first envisioned over 40 years ago, has been built on promises of delivering smaller, more efficient and cheaper electronic devices. 1 Due to the significant technological advances in the field, molecular thermoelectric materials in particular have seen an upsurge in interest in recent years. [2][3][4][5] It has been demonstrated, for instance, that quantum interference effects can be used to enhance the thermopower of singlemolecule junctions. 6-9 Furthermore, it has been shown how the molecular Seebeck coefficient can be tuned by varying the external environmental conditions. 10 Particularly encouraging, however, are the recent groundbreaking studies which achieved electrostatic control of thermoelectric single-molecule junctions, and consequently relatively large thermoelectric power factors (which quantify the amount of energy that can be generated from a given temperature difference between the leads). 11,12 Not only do these investigations open the door towards practical applications of molecular electronics but they also enable the exploration of the fundamental physics behind the thermoelectric energy conversion in nanoscale molecular

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Section: Devicesmentioning

confidence: 99%

Marcus Theory of Thermoelectricity in Molecular Junctions

2019

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“…Another issue is the inclusion of electron–phonon coupling in the description of heat transport. Although it has already been implemented within the NEGF approach to address electronic transport [ 154 , 155 , 156 , 157 , 158 ], there are not many atomistic-based studies related to their impact on phonon transport. Since the interaction with the electronic system will provide an additional energy exchange channel, it will be of interest to elucidate how some of the effects discussed in this review as well as in other investigations, such as thermal rectification and phonon filtering, will be modified by the inclusion of electron–phonon interactions.…”

Section: Discussionmentioning

confidence: 99%

Quantum Phonon Transport in Nanomaterials: Combining Atomistic with Non-Equilibrium Green’s Function Techniques

Sandonas

Gutiérrez

Cuniberti

2019

Entropy

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A crucial goal for increasing thermal energy harvesting will be to progress towards atomistic design strategies for smart nanodevices and nanomaterials. This requires the combination of computationally efficient atomistic methodologies with quantum transport based approaches. Here, we review our recent work on this problem, by presenting selected applications of the PHONON tool to the description of phonon transport in nanostructured materials. The PHONON tool is a module developed as part of the Density-Functional Tight-Binding (DFTB) software platform. We discuss the anisotropic phonon band structure of selected puckered two-dimensional materials, helical and horizontal doping effects in the phonon thermal conductivity of boron nitride-carbon heteronanotubes, phonon filtering in molecular junctions, and a novel computational methodology to investigate time-dependent phonon transport at the atomistic level. These examples illustrate the versatility of our implementation of phonon transport in combination with density functional-based methods to address specific nanoscale functionalities, thus potentially allowing for designing novel thermal devices.Entropy 2019, 21, 735 2 of 29 applications in nanoelectronics [7,8], renewable energy harvesting [9,10], nano-and optomechanical devices [11], quantum technologies [12,13], and therapies, diagnostics, and medical imaging [14].An important milestone in the field was the theoretically predicted [15] and subsequently measured quantization of the phononic thermal conductance in mesoscopic structures [16] at low temperatures, this result building the counterpart of the well-known quantization of the electrical conductance in quantum point contacts and other nanostructures (with conductance quantum given by e 2 /h, e being the electron charge and h Planck constant). Thermal conductance quantization has also been found in smaller nanostructures, such as gold wires, where quantized thermal conductance at room temperature was shown down to single-atom junctions [17,18]. The issue is, however, still a subject of debate (see, e.g., [19] for a recent discussion). In contrast to the electrical conductance quantization, the quantum of thermal conductance κ 0 depends, however, on the absolute temperature T through: κ 0 = π 2 k 2 B T/3h, with k B being the Boltzmann constant. This highlights a first important difference between charge and phonon transport. The second one is related to the different energy windows determining the corresponding transport properties: for electrons, the important window lies around the Fermi level, while, for phonons, the conductance results from an integral involving the full vibrational spectrum. Working with a broad spectrum of excitations poses major challenges when it comes to designing thermal devices such as cloaks and rectifiers [2,4], or for information processing in phonon-based computing [6].From the experimental perspective, it is obviously more difficult to tune heat flow than electrical currents. Unlike electrons, phonons are quasi-particle...

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“…The robustness of interference effects under vibron induced decoherence has been the focus of theoretical [74][75][76][77] as well as experimental investigation, 78,79 although mostly for nanojunction in strong coupling to the electrodes.…”

Section: Robustness Of Interference Effectsmentioning

confidence: 99%

Interference and shot noise in a degenerate Anderson-Holstein model

Donarini,

Niklas,

Grifoni

2020

Preprint

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We study the transport properties of an Anderson-Holstein model with orbital degeneracies and a tunneling phase that allows for the formation of dark states. The resulting destructive interference yields a characteristic pattern of positive and negative differential conductance features with enhanced shot noise, without further asymmetry requirements in the coupling to the leads. The transport characteristics are strongly influenced by the Lamb-shift renormalization of the system Hamiltonian. Thus, the electron-vibron coupling cannot be extracted by a simple fit of the current steps to a Poisson distribution. For strong vibronic relaxation, a simpler effective model with analytical solution allows for a better understanding and moreover demonstrates the robustness of the described effects.

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A Self Energy Model of Dephasing in Molecular Junctions

Cited by 12 publications

References 56 publications

Marcus Theory of Thermoelectricity in Molecular Junctions

Marcus Theory of Thermoelectricity in Molecular Junctions

Quantum Phonon Transport in Nanomaterials: Combining Atomistic with Non-Equilibrium Green’s Function Techniques

Interference and shot noise in a degenerate Anderson-Holstein model

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