Photo-induced directional transport in extended SSH chains

TL;DR

This work addresses current rectification in a nanoscale system by studying an extended SSH chain with trimerized hopping in a zigzag geometry under arbitrarily polarized light. The authors employ Floquet-Bloch theory with a vector potential $\mathbf{A}(\tau)$ and compute transport using nonequilibrium Green's functions within the Landauer-Büttiker framework, using $T(E) = \mathrm{Tr}[\Gamma_S G^r(E) \Gamma_D G^a]$ and $I(V) = \frac{2e}{h} \int_{E_F - eV/2}^{E_F + eV/2} T(E) dE$. Key findings show that light-induced anisotropy breaks inversion symmetry in the symmetric chain, enabling directional current and achieving rectification ratios above 90% under optimized light parameters, with rectification direction tunable by polarization. The results demonstrate a versatile, optically controllable platform for nanoscale rectifiers with potential applications in active optoelectronic devices.

Abstract

We investigate the current-voltage characteristics of an extended Su-Schrieffer-Heeger (SSH) chain under irradiation by arbitrarily polarized light, demonstrating its potential as a light-controlled rectifier. Irradiation of light induces anisotropy in the system, enabling directional current flow and active control of rectification behavior. Our analysis demonstrates that, under optimized light parameters, the rectification efficiency can exceed 90\%. Moreover, the direction of rectification-whether positive or negative-can be precisely controlled by varying the polarization of the light, highlighting the potential for external optical control of electronic behavior. The effect of light irradiation is incorporated using the Floquet-Bloch ansatz combined with the minimal coupling scheme, while charge transport is computed through the nonequilibrium Green's function formalism within the Landauer-Büttiker framework.

Figures (10)

• Figure 1: (Color online.) Schematic diagram of an extended SSH chain in presence of light irradiation, coupled to two 1D electrodes, source and drain. These electrodes are semi-infinite, metallic, and non-magnetic in nature. Each unit cell of the chain is indicated with a dotted box and composed of three sites. $t_1$ and $t_2$ are the intracell hopping integrals denoted with the green and red bonds, while $t_3$ is the the intercell hopping denoted with blue bonds. The different site colors represent the linear variation of on-site energies under the applied bias ${\mathcal{V}}$, as indicated by the horizontal colorbar. The irradiation effect is represented with the magenta waves.
• Figure 2: (Color online.) Top panel: Isotropic hopping configuration. Bottom panel: Anisotropic hopping configuration. (a), (c) Transmission probability as a function of energy at a bias ${\mathcal{V}}=0.5\,$Volt. (b), (d) Current-voltage characteristics. The number of unit cells is $N=7$. The hopping amplitudes for the isotropic case are fixed as $t_1=t_2=t_3=1\,$eV. For the anisotropic case $t_1 = 1\,$eV, $t_2 = 1.5\,$eV, and $t_3 = 1.25\,$eV. For the computation of the current, Fermi energy is fixed at $E_F =0.5\,$eV. Red and black colors denote the results for the forward and reverse bias conditions, respectively.
• Figure 3: (Color online.) Rectification ratio $RR$ as a function of voltage $V$. Black and red colors denote the results for the isotropic and anisotropic cases. The hopping amplitudes for the isotropic case are fixed as $t_1=t_2=t_3=1\,$eV. For the anisotropic case $t_1 = 1\,$eV, $t_2 = 1.5\,$eV, and $t_3 = 1.25\,$eV. The Fermi energy is fixed at $E_F =0.5\,$eV.
• Figure 4: (Color online.) (a) Transmission probability as a function of energy and (b) current as a function of voltage in the presence of light. The number of unit cells of the chain $N=7$. The hopping amplitudes are taken to be identical that is $t_1 = t_2 = t_3 = 1\,$eV. The Fermi energy is fixed at $E_F=0.5\,$eV. The light parameters are $A_x = 2.5$, $A_y = 0.5$, and $\phi = 0$. Red and black colors denote the results for the forward and reverse bias conditions, respectively.
• Figure 5: (Color online.) Rectification ratio as a function of voltage $V$ in the presence of light. All the systems parameters are identical to Fig. \ref{['Fig4']} that is the number of unit cells of the chain $N=7$. The hopping amplitudes are $t_1 = t_2 = t_3 = 1\,$eV. The Fermi energy is fixed at $E_F=0.5\,$eV. The light parameters are $A_x = 2.5$, $A_y = 0.5$, and $\phi = 0$.