Cu<sub>2</sub>FeS<sub>2</sub>: Discovery of an Exceptional Thermoplasmonic Semiconductor via Arrested Cation Exchange.

Li, Yuemei; Gu, Hongfei; Lu, Zexuan; Zhang, Haoqing; Su, Mengyao; Zhang, Xiuming; Liu, Jia; Shi, Wenxiong et al. · Adv Mater · 2026

basic_science · Level V

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Abstract

In this work, we report the discovery and cation exchange-mediated synthesis of Cu<sub>2</sub>FeS<sub>2</sub>, a compound predicted computationally but never observed in nature or realized in the laboratory. Our findings reveal that it possesses an anomalous electronic structure among analogous Cu-Fe-S semiconductors due to the unique valence configuration. More strikingly, this unprecedented material displays ultrahigh molar extinction coefficients (ε > 10<sup>7</sup> M<sup>-1</sup> cm<sup>-1</sup>) throughout the visible to near infrared (NIR) spectrum arising from remarkable localized surface plasmon resonances (LSPRs), coupled with intense electron-phonon interactions that enable ultrafast lattice heating on the 100 fs timescale. Such intrinsic attributes unequivocally designate Cu<sub>2</sub>FeS<sub>2</sub> as an ideal thermoplasmonic material. It demonstrates superior photothermal conversion efficiencies (PCE) spanning both visible and NIR wavelengths, outperforming assorted well-established photothermal materials including Au nanoparticles and MXene nanosheets. As a demonstration, we leverage its prominent thermoplasmonic functionality to drive efficient photothermal dry reforming of methane under low light intensities. Beyond the results presented here, Cu<sub>2</sub>FeS<sub>2</sub> is expected to provide a fertile ground for transformative investigations in many diverse fields of science.