Effects of Strain-Induced Pseudogauge Fields on Exciton Dispersion, Transport, and Interactions in Transition Metal Dichalcogenides Nanoribbons

Abstract

We study the effects of strain on exciton dynamics in transition metal dichalcogenide (TMD) nanoribbons. Using the Bethe-Salpeter formalism, we derive the exciton dispersion relation in strained TMDs and demonstrate that strain-induced pseudo-gauge fields significantly influence exciton transport and interactions. Our results show that low-energy excitons occur at finite center-of-mass momentum, leading to modified diffusion properties. Furthermore, the exciton dipole moment depends on center-of-mass momentum, which enhances exciton-exciton interactions. These findings highlight the potential of strain engineering as a powerful tool for controlling exciton transport and interactions in nanoribbon-based TMD optoelectronic and quantum devices.

Figures (9)

• Figure 1: Schematic illustration of a strained monolayer TMD nanoribbon. The nanoribbon is finite along the y-direction (width $L_y$) and translationally invariant along the x-direction (length). The applied strain bends the ribbon into an arc shape described by the displacement field $(u_x, u_y) = (xy/R, -x^2/2R)$, where $R$ is the radius of curvature. This deformation generates a position-dependent pseudogauge field that modifies the electronic band structure. The trigonal basis function $T_n(y)$ is defined as $T_n(y) = L_y - |y - y_n|(N + 1)$, where $|y| < L_y/2$, and $y_n = L_y\left(\frac{n}{N+1} - \frac{1}{2}\right)$ is the position of the $n$-th basis function. $N$ is the number of basis functions, and $L_y$ is the width of the nanoribbon along the y-direction. This function is used to satisfy the hard boundary conditions for an arc-shaped monolayer Transition Metal Dichalcogenides (TMDs) system. We note that $\langle T_n | T_{n+1} \rangle \ne 0$.
• Figure 2: (a): Quasiparticle energy dispersion of monolayer MoS$_2$ nanoribbon around $k_x = 0$, for unstrained case, $\eta = 0$, and arc-shaped strained cases, $\eta \neq 0$. We set the width of the nanoribbon to be $L_y=a_0(N+1)$ with $N=20$, and arc radius $R=0.5 L_y$. (b): Probability density $|\psi(y)|^2$ of the conduction (CB) and valence (VB) bands and two edge states, plotted against the coordinate $y \in (0,Na_0)$ with $N=20$ while setting $k_x$ close to zero. At $\eta=1$, the edge states hybridize and extend fully into the bulk, losing their characteristic edge state signature; these hybridized states are denoted as ES$^*$. (c): Comparison of the energy gaps between the first two conduction bands in unstrained ($\eta=0$) and strained systems($\eta=1$): The finite-size gap in the unstrained system is 116 meV ($T=1346$ K), while the strain-induced gap in the strained system increases significantly to 365 meV ($T=4235$ K) for the $\eta=1$ case.
• Figure 3: Non-topological quasiparticle energy dispersion of monolayer MoS$_2$ nanoribbon around $k_x = 0$, for unstrained case, $\eta = 0$, and arc-shaped strained cases, $\eta \neq 0$. In this figure, the Chern number is set to zero.
• Figure 4: Exciton energy as a function of center-of-mass momentum $Q_x$ (scaled by $a_0$), resulting from transitions between the valence band (VB) and conduction band (CB): (a) in the absence of strain and (b) in the presence of strain. The magenta plus symbols represent interacting exciton states, while the blue open circles represent non-interacting exciton states. $N=20$ is used in the calculations. The inset shows a zoomed-in view of the low-energy exciton states.
• Figure 5: Exciton energy as a function of center-of-mass momentum $Q_x$ (multiplied by $a_0$) in the non-topological unstrained and non-topological strained cases. In this figure, the Chern number is set to zero.