Floquet-driven tunneling control in monolayer MoS$_2$

TL;DR

This work addresses photon-assisted quantum transport in monolayer MoS$_2$ under a time-periodic (Floquet) laser drive across a static potential barrier. It combines an analytical Floquet treatment for the central band $E$ and first sidebands $E \pm \hbar\omega$ with a transfer-matrix approach for higher-order channels to compute transmission, using boundary matching and current-density conservation. Key findings show the central Floquet band yields the largest transmission, while the laser induces spin-dependent oscillations and activates photon-exchange channels that reduce total transmission as the driving strength $\alpha$ increases; the effect is enhanced for wider barriers and off-normal incidence. The results demonstrate a route to optically tunable filtering and spintronic control in driven MoS$_2$, with potential applications in sensitive electromagnetic sensing and advanced optoelectronic devices in van der Waals materials.

Abstract

We study how fermions in molybdenum disulfide MoS$_2$ interact with a laser field and a static potential barrier, focusing on the transmission probability. Our aim is to understand and control photon-assisted quantum transport in this two-dimensional material under external driving. We use the Floquet approximation to describe the wave functions in the three regions of the system. By applying continuity conditions at the boundaries, we obtain a set of equations involving an infinite number of Floquet modes. We explicitly determine transmissions involving the central band $E$ and the first sidebands $E \pm \hbarω$. As for higher-order bands, we use the transfer matrix approach together with current density to compute the associated transmissions. Our results reveal that the transmission probability oscillates for both spin-up and spin-down electrons. The oscillations of spin-down electrons occur over nearly twice the period of spin-up electrons. Among all bands, the central one consistently shows the highest transmission. We also find that stronger laser fields and wider barriers both lead to reduced transmission. Moreover, laser irradiation enables controllable channeling and filtering of transmission bands by tuning the laser intensity and system parameters. This highlights the potential of laser-driven MoS$_2$ structures for highly sensitive electromagnetic sensors and advanced optoelectronic devices.

Figures (7)

• Figure 1: A schematic of a monolayer MoS$_2$ sheet is shown. A static potential barrier of height $V_0$ is applied to the central region of width $D$, which is exposed to a laser field with amplitude $A_0$ and frequency $\omega$.
• Figure 2: Transmission spin-up ($s_z=1$: red solid line) and spin-down ($s_z=-1$: black dashed line) for the valley $K$ as a function of the barrier height $V_0$ for three different incident angles $(\phi = 0^\circ, 30^\circ, 45^\circ)$, laser frequency $\omega = 15 \times 10^{12}$ Hz, parameter $\alpha = \frac{ev_F A_0}{\hbar \omega}= 1$, incident energy $E = 1.2$ eV, and barrier width $D = 5$ nm.
• Figure 3: Transmissions spin-up ($s_z=1$) of the central band $T_0$ and the first five sidebands ($l=\pm1, \cdots,\pm 5$) as a function of the parameter $\alpha = \frac{ev_F A_0}{\hbar \omega}$ for three incident energies ($E=1.2$ eV, 1.4 eV, 1.6 eV), $\omega = 15 \times 10^{12}$ Hz, $\phi=0$, $D=10$ nm, and $V=2.6$ eV
• Figure 4: Total transmission spin-up ($s_z=1$: red solid line) and spin-down ($s_z=-1$: black dashed line) as a function of the incident angle $\phi$ in $n$–$p$–$n$ junction for three laser field parameters ($\alpha=0, 1, 3$), $E=1.2$ eV, $V_0=2.6$ eV, $\omega=12 \times 10^{12}$ Hz, and $D=10$ nm.
• Figure 5: Total transmission as a function of the incident angle $\phi$ for n–n–n junction ($E = 1.2$ eV, $V_0 = 0.05$ eV) (red), p–p–p junction ($E = -1.2$ eV, $V_0 = -0.05$ eV) (black), three laser parameters ($\alpha = 0,1,3$), $D = 10$ nm. The solid lines (dashed lines) correspond to spin-up (spin-down).