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Fibonacci-Engineered Spin and Charge Thermoelectrics in a Long Range Su-Schrieffer-Heeger Chain: A Pathway to Giant Figure of Merit

Ranjini Bhattacharya, Souvik Roy

TL;DR

This work tackles the challenge of achieving high-efficiency thermoelectric conversion in low-dimensional systems by engineering spin-selective transport in an extended SSH chain with Fibonacci-type onsite modulation and cosine-tuned nearest- and next-nearest-neighbor hopping. Using a tight-binding model combined with non-equilibrium Green's function techniques, the authors compute spin-resolved transmission and Landauer-based thermoelectric coefficients, demonstrating strong spin filtering and a dominant spin Seebeck response. The study reports large spin figures of merit $Z_S T$ (often exceeding the charge counterpart $Z_C T$) across broad parameter ranges, with peak values reaching and surpassing $Z_S T \sim 20$–$58$ in various scans, and Seebeck coefficients $S_S$ up to several hundred microvolts per kelvin. The results substantiate a robust, tunable pathway to high-performance spin-based thermoelectrics in aperiodic, quasi-1D topological lattices, with implications for experimental realization in cold-atom or molecular-assembly platforms.

Abstract

In this work, we present a novel investigation into the spin-dependent thermoelectric performance of an extended Su-Schrieffer-Heeger (SSH) model, showcasing for the first time how its intrinsic spin filtration mechanism can be strategically harnessed to function as an efficient spin thermoelectric generator. By introducing a Fibonacci-type aperiodic modulation in the onsite energies, we engineer a deterministic disorder that mimics realistic aperiodic systems and profoundly influences transport characteristics. Furthermore, we incorporate both nearest-neighbor (NN) and next-nearest-neighbor (NNN) hopping amplitudes with tunable cosine dependencies, enabling us to meticulously explore the intricate interplay between these hopping processes and its implications on thermoelectric behavior. Our analysis reveals a remarkable enhancement in the dimensionless thermoelectric figure of merit ZT for both charge and spin transport channels, under carefully optimized conditions. Notably, the spin thermoelectric response exhibits distinct advantages, opening a new frontier in the design of next-generation thermoelectric materials and devices. This qualitative study not only deepens our understanding of aperiodic topological systems but also establish a foundational framework for exploiting spin-based thermoelectricity in low-dimensional platforms.

Fibonacci-Engineered Spin and Charge Thermoelectrics in a Long Range Su-Schrieffer-Heeger Chain: A Pathway to Giant Figure of Merit

TL;DR

This work tackles the challenge of achieving high-efficiency thermoelectric conversion in low-dimensional systems by engineering spin-selective transport in an extended SSH chain with Fibonacci-type onsite modulation and cosine-tuned nearest- and next-nearest-neighbor hopping. Using a tight-binding model combined with non-equilibrium Green's function techniques, the authors compute spin-resolved transmission and Landauer-based thermoelectric coefficients, demonstrating strong spin filtering and a dominant spin Seebeck response. The study reports large spin figures of merit (often exceeding the charge counterpart ) across broad parameter ranges, with peak values reaching and surpassing – in various scans, and Seebeck coefficients up to several hundred microvolts per kelvin. The results substantiate a robust, tunable pathway to high-performance spin-based thermoelectrics in aperiodic, quasi-1D topological lattices, with implications for experimental realization in cold-atom or molecular-assembly platforms.

Abstract

In this work, we present a novel investigation into the spin-dependent thermoelectric performance of an extended Su-Schrieffer-Heeger (SSH) model, showcasing for the first time how its intrinsic spin filtration mechanism can be strategically harnessed to function as an efficient spin thermoelectric generator. By introducing a Fibonacci-type aperiodic modulation in the onsite energies, we engineer a deterministic disorder that mimics realistic aperiodic systems and profoundly influences transport characteristics. Furthermore, we incorporate both nearest-neighbor (NN) and next-nearest-neighbor (NNN) hopping amplitudes with tunable cosine dependencies, enabling us to meticulously explore the intricate interplay between these hopping processes and its implications on thermoelectric behavior. Our analysis reveals a remarkable enhancement in the dimensionless thermoelectric figure of merit ZT for both charge and spin transport channels, under carefully optimized conditions. Notably, the spin thermoelectric response exhibits distinct advantages, opening a new frontier in the design of next-generation thermoelectric materials and devices. This qualitative study not only deepens our understanding of aperiodic topological systems but also establish a foundational framework for exploiting spin-based thermoelectricity in low-dimensional platforms.
Paper Structure (24 sections, 24 equations, 18 figures, 1 table)

This paper contains 24 sections, 24 equations, 18 figures, 1 table.

Table of Contents

  1. Introduction
  2. Theoretical Framework
  3. Quantum Design of Thermoelectric Transport: System Architecture and Hamiltonian Framework
  4. Quantum Transport in Ferromagnetic SSH Chains: Tight-Binding Hamiltonian Formalism
  5. Theoretical framework
  6. Numerical Results and Discussion
  7. Spectral Profile of the Transmission Function
  8. Seebeck Coefficient
  9. Electrical and thermal conductances
  10. Charge and spin figure of merits ($Z_CT$, $Z_ST$)
  11. Tuning Maximum Thermoelectric Quantities via $\delta$
  12. Dependence of Maximum Thermoelectric Parameters on $\beta$
  13. Variation of maximum values of thermoelectric parameters with $g_a$
  14. Dependence of Maximum Values of Thermoelectric Parameters on $g_b$
  15. Exploring the Maximum values of Thermoelectric Parameters with $\eta$
  16. ...and 9 more sections

Figures (18)

  • Figure 1: (Color online). The schematic illustration presents a long range Su-Schrieffer-Heeger (SSH) chain symmetrically connected to source and drain electrodes, where the site energy profile is engineered through a Fibonacci modulation for a specific generation. This unique configuration opens a new frontier in thermoelectric transport by capturing interplay between NN and NNN hopping with aperiodicity.
  • Figure 2: (Color online). The plot illustrates the transmission function as a function of energy under various hopping configurations. Panel (a) displays fully spin-resolved transmission spectra, highlighting complete separation between up and down spin channels under nearest-neighbor (NN) hopping. In contrast, panel (b) shows partial overlap between the spin-resolved channels, still within the NN hopping-only framework. Panel (c) incorporates next-nearest-neighbor (NNN) hopping and again reveals complete spin-channel separation, indicating the strong influence of longer-range hopping. Finally, panel (d) includes both NN and NNN hoppings, resulting in overlapping transmission lines, thereby capturing the interplay between the two hopping mechanisms and their collective impact on spin-resolved transport.
  • Figure 3: (Color online). Seebeck coefficient as a function of Fermi energy is shown. Panel (a) highlights the spin-resolved Seebeck response, with distinct contributions from up-spin and down-spin channels. Panel (b) presents the corresponding charge and spin Seebeck coefficients, capturing the overall thermoelectric behavior across both transport modes.
  • Figure 4: (Color online). Spin-resolved electronic conductance as a function of Fermi energy is presented in panel (a), highlighting distinct contributions from up- and down-spin carriers. Panel (b) contrasts the total charge and spin conductances, providing insight into the system’s thermoelectric response under varying transport channels.
  • Figure 5: (Color online). Thermal conductance as a function of Fermi energy, the parameters used in this analysis are consistent with those in Fig. \ref{['fig1']} (d). This offers a complete perspective on the thermoelectric transport characteristics of the system.
  • ...and 13 more figures