FisMat2017 - Submission - View

Abstract's title: Thermoelectric efficiency of molecular junctions
Submitting author: Carmine Antonio Perroni
Affiliation: Dipartimento di Fisica "E. Pancini" and CNR SPIN
Affiliation Address: Via Cinthia, I-80126 Napoli, Italy
Country: Italy
Oral presentation/Poster (Author's request): Oral presentation
Other authors and affiliations: Domenico Ninno, Vittorio Cataudella
Abstract

Focus of the talk is on experimental set-ups and theoretical studies  concerning thermoelectric performances of molecular junctions. In addition to charge conductance, the thermoelectric parameter commonly measured in these systems is the thermopower, which is typically rather low. Recent experimental outcomes are relative to several  junction configurations used to optimize the thermopower. On the other hand, theoretical calculations provide estimations of all the thermoelectric parameters in the linear and non-linear regime, in particular of the thermoelectric figure of merit and efficiency [1]. For this reason, the talk will mainly focus on theoretical studies analyzing the role of not only electronic, but also of the vibrational degrees of freedom [2,3,4].

Theoretical results in the coherent regime are discussed considering in particular a reference simple model with one electronic level and one vibrational mode in order to provide the relevant orders of magnitude for the thermoelectric properties. Moreover, we analyze the effects of molecular many-body interactions, such as electron-vibration couplings, which typically tend to reduce the efficiency [2]. Indeed, the electron–vibration interaction can enhance both phonon and electron thermal conductance, and it can reduce not only the charge conductance, but also the thermopower. For prototype fullerene junctions, we focus on the results obtained within a non-equilibrium adiabatic approach which includes a strong Coulomb repulsion and applies to the self-consistent calculation of electron and phonon transport properties of massive molecules within the Coulomb blockade regime [3]. In particular, the effect of the strong electron–electron interactions provides a peculiar double-peak structure to the thermopower versus charge conductance curve.

Within the regime of weak to intermediate electron–vibration and vibration–lead phonon coupling, the peak values of the thermoelectric figure of merit are slightly less than unity, and the maximal efficiency of the junction can reach values slightly less than half of the Carnot limit for large temperature differences between the leads. Since a fine tuning of many parameters and coupling strengths is required to optimize the thermoelectric conversion in molecular junctions, new theoretically proposed set-ups are mentioned providing the new research directions in the field of molecular thermoelectricity [4].

 

References:

[1] A. Nocera, C.A. Perroni, V. Marigliano Ramaglia, and V. Cataudella, Beilstein J. Nanotechnol., 7 (2016) 439.

[2] C.A. Perroni, D. Ninno, and V. Cataudella, Phys. Rev. B, 90 (2014) 125421.

[3] C.A. Perroni, D. Ninno, and V. Cataudella, New J. Phys., 17 (2015) 083050.

[4] C.A. Perroni, D. Ninno, and V. Cataudella, invited Topical Review on “Thermoelectric efficiency of molecular junctions”, J. Phys. : Condens. Matter. 28 (2016) 373001