Thermoelectric Enhancement via Electronic and Phononic Channels in Staggered and Non-Staggered Dimerized Quantum Ring

TL;DR

This work investigates thermoelectric performance in Su–Schrieffer–Heeger rings with dimerized hopping subjected to Aubry–André–Harper quasiperiodic on-site modulations. Using nonequilibrium Green's function methods in the linear-response regime, it shows that engineered hopping asymmetry, topological band structure, and quasiperiodic disorder produce energy-dependent transmission features that sharply enhance the Seebeck coefficient while maintaining usable electrical conductance. The study maps how disorder strength, dimerization, and lead geometry shape $G$, $S$, $K_ ext{el}$, and $K_ ext{ph}$, revealing parameter regimes with $ZT$ values up to around 27–28, driven by energy filtering and transmission asymmetry. These results offer actionable design principles for nanoscale thermoelectrics in molecular-scale rings, including the utility of asymmetric lead coupling and controlled quasiperiodic modulation to approach high-efficiency energy conversion.

Abstract

Harnessing the quantum coherence and tunability of molecular-scale structures, we theoretically explore thermoelectric transport in ring-shaped molecular junctions featuring dimerized hopping integrals. By engineering alternating strong and weak bonds in both staggered and non-staggered configurations, we reveal a marked transmission asymmetry that drives a substantial enhancement in the thermoelectric figure of merit, ZT. To further steer transport behavior, we introduce controlled aperiodicity via site-energy modulations in unit cell format governed by the Aubry-André-Harper (AAH) potential, a quasiperiodic landscape that enables tunable localization-delocalization transitions. This interplay between hopping dimerization and AAH-type disorder gives rise to energy filtering effects and a rich spectrum where extended and critical states coexist, amplifying the Seebeck coefficient while preserving finite electrical conductance. Through a comprehensive non-equilibrium Green's function analysis, we uncover how key device parameters, including disorder strength, dimerization amplitude, and lead-ring connectivity, collectively shape transport characteristics. Notably, asymmetric lead couplings are shown to enhance performance by leveraging quantum interference pathways. Our findings highlight a robust design strategy for optimizing nanoscale thermoelectric functionality, providing actionable insights for experimental realization in molecular electronic platforms.

Figures (15)

• Figure 1: (Color online) The schematic diagram depicts SSH ring symmetrically coupled to source and drain electrodes. In this configuration, the onsite energies are modulated with AAH potential. This setup highlights how the interplay of hopping strengths and AAH potential provides a framework for effective enhancement of thermoelectric efficiency.
• Figure 2: (Color online) The schematic diagram depicts phononic SSH ring symmetrically coupled to source and drain electrodes. In this configuration, the mass is modulated with AAH potential.
• Figure 3: (Color online) Transmission function $\mathcal{T}(E)$ plotted as a function of electron energy $E$. (a) and (b) correspond to the non-staggered AAH potential: panel (a) illustrates the case $t_1/t_2 > 1$, while panel (b) shows $t_1/t_2 < 1$, for two onsite potential strengths $W = 0.3$ and $W = 1.3$. (c) and (d) depict the same scenarios for the staggered AAH potential.
• Figure 4: (Color online) Electronic conductance $G$ as a function of the Fermi energy $E_F$. Panels (a) and (b) correspond to non-staggered AAH potentials with $t_1/t_2 > 1$ and $t_1/t_2 < 1$, respectively. Panels (c) and (d) show the corresponding results for the staggered case. In each panel, conductance is plotted for two values of onsite disorder strength: $W = 0.3$ (pink) and $W = 1.3$ (green).
• Figure 5: (Color online) Seebeck coefficient $S$ as a function of the Fermi energy $E_F$. Panels (a) and (b) correspond to non-staggered cases with $t_1/t_2 > 1$ and $t_1/t_2 < 1$, respectively. Panels (c) and (d) depict the staggered configurations for the same hopping ratios. The onsite disorder strengths are $W = 0.3$ (pink) and $W = 1.3$ (green).