Dissipation effects in the Su-Schrieffer-Heeger model coupled to a metallic environment

TL;DR

This paper models a trans-polyacetylene molecule on a metallic substrate using a modified SSH model with dissipation effects, revealing a metal-insulator transition and local phase nucleation relevant for nanoelectronics.

Contribution

It introduces a generalized SSH model incorporating metallic environment effects, predicting phase transitions and local phase nucleation in tPA molecules on metallic surfaces.

Findings

Homogeneous substrate causes a zero-temperature insulator-to-metal transition.

Inhomogeneous substrates lead to local nucleation of metallic or dimerized phases.

Results aid interpretation of tPA/Cu(110) experiments and device design.

Abstract

We theoretically study the electronic and lattice properties of a trans-polyacetylene (tPA) molecule deposited on top of a metallic substrate at equilibrium. We describe the system using a modified Su-Schrieffer-Heeger (SSH) model generalized to incorporate the effects of a metallic environment, represented by independent one-dimensional semi-infinite chains coupled to each site of the SSH chain (i.e., ``local bath approximation"). We focus on the zero-temperature case and obtain the physical properties of an $N$-site tPA chain deposited on a metallic surface by minimizing its total ground-state energy (i.e., electronic plus lattice degrees of freedom) as a function of the $N$ lattice-site positions. Interestingly, in the case of a homogeneous metallic substrate, where all coupling parameters are assumed identical, the SSH chain undergoes a zero-temperature insulator-to-metal transition as the coupling parameter $\gamma_0$ reaches a critical value where the Peierls dimerization is fully suppressed and the system becomes metallic. In addition, our model can be generalized to describe inhomogeneous situations where the substrate contains metallic and insulating regions, as usually occurs in realistic experiments containing accidentally oxidized decoupling layers. In this case, our results predict the occurrence of local nucleation of the metalized or the Peierls-dimerized phase within the same tPA molecule, depending on whether the surface directly beneath the molecule is metallic or insulating, respectively. We finally discuss the relevance of our findings for both the correct interpretation of existing tPA/Cu(110) experiments, as well as for their possible utility in the design of novel organic nanoelectronic devices.