【摘要】 拓扑量子材料是一类因电子间强关联作用而呈现出奇异物态并具有独特拓扑能带结构的材料体系。非线性光谱技术作为研究材料静态性质与光诱导超快动力学的有力手段，在揭示此类材料的微观机制方面发挥着关键作用。研究拓扑量子材料的太赫兹辐射特性，对厘清体系内准粒子与元激发的耦合作用具有重要理论价值，同时也为新型太赫兹辐射器件的开发开辟了应用方向。本文介绍了利用飞秒激光激发拓扑量子材料产生太赫兹辐射的实验方法及其物理机制。相关研究不仅深化了对拓扑物态中光-物质相互作用的理解，也为发展高性能、新原理的太赫兹辐射源开辟了新的技术路径。更多还原

【Abstract】 Significance The terahertz（THz） spectral regime（0.1-10 THz）, lying between the microwave and infrared regions, holds immense potential for transformative applications in ultra-high-speed wireless communications, non-destructive imaging, and molecular spectroscopy. However, the efficient generation of broadband, tunable, and high-power THz waves remains a significant technological challenge. Traditional methods, such as photoconductive antennas and optical rectification in nonlinear crystals, often suffer from limitations in bandwidth, conversion efficiency, or tunability. The recent emergence of topological materials—a class of matter in which global wavefunction topology governs robust electronic properties—has opened a revolutionary pathway for THz photonics. These materials, including topological insulators and topological semimetals, possess unique electronic structures characterized by Dirac-like linear band dispersions, spin-momentum locking, and large Berry curvature effects. These features give rise to highly efficient, ultrafast nonlinear photocurrents under femtosecond laser excitation, rendering them exceptional platforms for novel high-performance THz emitters. Research in this field not only aims to develop next-generation THz sources but also employs THz emission spectroscopy as a powerful, noninvasive probe to unravel the fundamental symmetries, band topology, and ultrafast carrier/spin dynamics inherent to these exotic quantum states.Progress Significant progress has been achieved across different families of topological materials, each harnessing distinct physical mechanisms. In topological insulators such as Bi₂ Se₃ and Sb₂ Te₃, topologically protected surface states with spin-momentum locking play a pivotal role. Circularly polarized light can selectively excite spin-polarized carriers, generating photocurrents via the circular photogalvanic effect（CPGE）, which is ideal for producing chiral THz radiation. Moreover, shift currents and optical spin orientation contribute to ultrafast THz emission. Pioneering time-resolved THz emission spectroscopy has quantitatively decoupled the contributions from surface-state CPGE and ultrafast displacement currents in doped Bi₂ Se₃. Studies have shown that suppressing bulk conductivity enhances surface-state-dominated THz emission, and precise control over pump polarization and sample orientation enables the generation of highly tunable chiral THz waves from materials such as Bi₂ Se₃ nanofilms.An even richer variety of mechanisms emerges in topological semimetals, where gapless bulk states participate directly. Dirac semimetals exhibit diverse dominant mechanisms. In graphene, a prototypical 2D Dirac semimetal, the photon-drag effect can be dominant under suitable excitation conditions, in which photon momentum transfer drives a transient current. Notably, THz emission from graphene can be drastically enhanced and actively modulated via substrate engineering or electrostatic gating in heterostructures such as graphene/SiO₂/Si, demonstrating its potential as a programmable THz modulator. In contrast, for three-dimensional Dirac semimetals like Cd₃ As₂, the photothermoelectric effect can contribute significantly alongside nonlinear photocurrents, yielding THz signals with a distinct sub-linear dependence on pump fluence. Intriguingly, competing mechanisms can emerge in the same material depending on sample quality and excitation conditions, highlighting the complex interplay of different photonic processes. Weyl semimetals, exemplified by TaAs, are outstanding platforms for chiral THz generation. Their broken inversion symmetry and paired Weyl nodes of opposite chirality enable a giant CPGE. Circularly polarized light selectively excites carriers at a specific chiral node, and the tilting of Weyl cones leads to a net velocity imbalance, producing helicity-dependent photocurrents. This behavior has been clearly demonstrated in TaAs, while in chiral topological semimetals such as CoSi and RhSi—which lack all mirror symmetries—record-high CPGE responses approaching the theoretical limit have been observed. Emerging studies on nodal-line semimetals and triple-point semimetals reveal that their higher-dimensional band degeneracies and strong crystal anisotropy can also induce pronounced, symmetry-governed THz emission. Furthermore, constructing heterostructures with magnetic layers leverages efficient spin-to-charge conversion at topological interfaces, generating strong THz pulses controllable by spin and charge currents.Conclusions and Prospects Topological materials have firmly established themselves as a versatile and powerful material platform for THz generation and manipulation. Their defining characteristics—topologically protected surface/edge states, linear band dispersions, and strong Berry curvature effects—enable highly efficient nonlinear optical conversion and provide unprecedented control knobs（e. g., light polarization, electrostatic gating, magnetic fields） for regulating the amplitude, polarity, and chirality of emitted THz waves. Looking ahead, several critical challenges and promising opportunities define the future trajectory of this field. Key challenges include the quantitative separation of competing bulk and surface photocurrent mechanisms, the considerable discrepancy between measured and theoretically predicted CPGE magnitudes in certain systems, and the transition from proof-of-concept pulsed emission to practical continuous-wave THz devices. Future research will likely focus on advanced material engineering to purify topological phases, the exploration of more complex systems such as intrinsic magnetic topological insulators（e.g., Mn Bi₂Te₄） and Moiré heterostructures where topology intertwines with electronic correlations, and the development of integrated THz devices. In addition, THz emission spectroscopy will continue to evolve as an indispensable tool for the noninvasive, ultrafast characterization of symmetry breaking, topological phase transitions, and quantum geometric properties in this rapidly expanding class of quantum materials. The synergy between fundamental investigations of topological phenomena and the engineering of their photonic responses is poised to drive innovations in compact, tunable, and high-efficiency THz technologies for future information and sensing applications.更多还原