[Paper Review] Chiral Terahertz Amplification and Lasing using Two-Dimensional Materials with Berry Curvature Dipole

Amin Hakimi, J. Sebastian Gomez-Diaz+1 more|arXiv (Cornell University)|Mar 6, 2026

Metamaterials and Metasurfaces Applications0 citations

TL;DR

The paper proposes and analyzes a cavity-based, DC-biased two-dimensional material platform with Berry curvature dipole to achieve tunable THz amplification and lasing, using a single low-symmetry 2D layer (e.g., twisted bilayer graphene) at the center of a Fabry–Pérot cavity.

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.

Motivation & Objective

• Motivate the need for compact, electrically driven coherent THz sources within the THz gap.
• Introduce a cavity-based gain mechanism using Berry curvature dipole (BCD) in a DC-biased 2D material.
• Establish the physical principles, operating conditions, and parameter regimes for BCD-enabled THz gain and lasing.
• Show that a single low-symmetry 2D layer can provide substantial amplification and enable polarization-selective emission.
• Provide analytical and numerical guidance for future experimental realizations across the THz band via cavity tuning.

Proposed method

• Model the 2D material conductivity with a BCD-induced non-Hermitian and gyrotropic form as a function of DC bias, frequency, and scattering rate.
• Use a transfer-matrix formalism to derive the forward transfer matrix of the 2D layer and compute reflection, transmission, and absorptance for circularly polarized excitation.
• Place a single 2D layer with BCD at the center of a Fabry–Pérot cavity with DBR mirrors and analyze amplified transmittance and negative absorptance.
• Perform complex-frequency modal analysis to identify lasing thresholds via the condition D(ω)=0 and distinguish two resonance classes.
• Provide approximate analytical expressions for thresholds in high-frequency (low-loss) and low-frequency (high-loss) regimes.

Experimental results

Research questions

• RQ1 Under what conditions can a DC-biased 2D material with Berry curvature dipole provide THz gain within a cavity?
• RQ2 How do cavity length, mirror reflectivity, and material loss affect amplification and lasing thresholds?
• RQ3 Can a single 2D layer yield chiral, polarization-selective THz gain, and how is handedness controlled by bias sign?
• RQ4 What are the dominant resonant modes and their interaction with the BCD-induced gain in a FP cavity?
• RQ5 What practical guidance emerges for achieving tunable, scalable THz sources across the 0.1–10 THz range?

Key findings

• Amplification and even lasing are achievable when a DC-biased 2D material with BCD is placed at the cavity center, interacting predominantly with odd FP modes.
• The sign of the gain parameter ξ (proportional to the DC bias) selects the polarization eigenstate that experiences gain, enabling bias-tunable chiral emission.
• Increasing cavity quality factor, bias magnitude, or operating at higher-order odd modes enhances amplification and mitigates damping.
• A single 2D layer (e.g., twisted bilayer graphene) can provide substantial THz gain without stacking multiple layers, preserving scalability via cavity-length tuning.
• The framework shows robust amplification across a range of γ (loss) values and allows compensation via higher DBR reflectivity or larger ξ, with polarization preserved (negligible cross-polarization).
• Lasing thresholds are analyzed via complex-frequency resonance conditions, yielding two resonance families, one capable of providing gain that can compensate cavity losses.