Chiral Terahertz Amplification and Lasing using Two-Dimensional Materials with Berry Curvature Dipole

Abstract

Compact, electrically driven sources of coherent terahertz (THz) radiation remain a challenge due to the lack of efficient gain media and scalable device platforms. Here, we propose and theoretically investigate a cavity-based THz gain mechanism enabled by Berry curvature dipole (BCD) in a DC-biased, low-symmetry two-dimensional (2D) material. Placing the biased 2D layer at the center of a Fabry-Perot cavity enhances light-matter interactions, enabling direct conversion of DC electrical power into coherent THz radiation. We analyze the conditions for amplification and lasing, and identify the parameter regimes that support self-oscillatory coherent emission. Rather than introducing a specific device implementation, our work establishes the physical principles and operating conditions for BCD-enabled THz gain and lasing and provides the theoretical foundation for future realizations. The chiral nature of BCD-induced response enables bias-tunable chiral optical gain, selective polarization eigenstate amplification, and electrically controlled handedness of the emitted radiation. Importantly, substantial amplification and lasing are achieved using only a single 2D material, significantly simplifying device design while preserving scalability across the THz band via cavity-length tuning. This platform is broadly applicable to low-symmetry 2D materials with finite BCD, offering a general route toward compact, frequency-tunable, and polarization-selective THz sources.

Figures (12)

• Figure 1: Schematic of a cavity enhancing light-matter interactions in a DC-biased 2D material exhibiting BCD. The cavity is closed at both ends by partially reflecting mirrors.
• Figure 2: Schematic of a Fabry-Pérot cavity enhancing light-matter interactions with a 2D material with BCD positioned at its center, and distributed Bragg reflectors (DBRs) placed at both ends acting as partially reflective mirrors. The longitudinal electric field profiles for odd-order resonances ($q=1,3,5$) are shown, highlighting a field maximum at the cavity center. The 2D material with BCD is DC-biased, generating a transverse drift current resulting in optical chiral gain, with amplification controlled by the applied DC bias.
• Figure 3: Geometry of the structure used in the transfer-matrix derivation. A 2D material with surface conductivity $\overline{\boldsymbol{\sigma}}(\omega)$ is sandwiched between two dielectric layers with different dielectric constants. Forward- and backward-propagating waves are shown on both sides of the 2D material.
• Figure 4: Reflectance, transmittance, and absorptance of the platform proposed in Fig. \ref{['fig:Structure']} for various values of the gain parameter $\xi$ of the TBG layer located at the center. DBR mirrors are at both ends as shown in Fig. \ref{['fig:Structure']}. The first row (a–c) shows results for an RCP incident wave. The second row (d–f) provides a zoomed view near the fundamental resonance at 0.5 THz. The third row (g–i) presents the results for an LCP incident wave. The parameters for (a–i) are: $\varepsilon_{\rm d}=4$, $\omega_{\rm F}/(2\pi)=0.24\:\mathrm{THz}$, $\gamma=10^{12}\:{\rm s}^{-1}$, $\rho=-0.9$, and $L = 149.90 \: \mu{\rm m}$. The fourth row (j–l) corresponds to an RCP incident wave in the same cavity, but with increased TBG losses ($\gamma=5\times10^{12}\:{\rm s}^{-1}$) and higher DBR reflectivity ($\rho=-0.95$). Amplification is seen in various cases.
• Figure 5: (a) Reflectance, (b) transmittance, and (c) absorptance of the proposed FP cavity when it is illuminated by an RCP incident field. Results are plotted for various values of the DBRs' reflectivity coefficient $\rho_0$. The parameters are: $\varepsilon_{\rm d}=4$, $\omega_{\rm F}/(2\pi)=0.24\:\mathrm{THz}$, $\gamma=10^{12}\:{\rm s}^{-1}$, $\xi/\omega_{\rm F} = 5$, and $L=149.90 \: \mu {\rm m}$.