Probing strong electron-phonon coupling in semimetallic PtSe₂ via ultrafast optical spectroscopy

Abstract

Platinum diselenide (PtSe₂) exhibits a distinctive thickness-modulated metal-to-semiconductor transition, which makes it suitable for diverse applications in nanoelectronics and optoelectronics. This study systematically investigates the spatiotemporal dynamics of photoexcited carrier relaxation in PtSe₂. Through temperature-dependent ultrafast spectroscopy, two distinct low-frequency acoustic phonons (AP) were identified in multilayer PtSe₂. Transient absorption microscopy (TAM) measurements reveal thickness-dependent relaxation dynamics and distinct carrier diffusion behavior in multilayer PtSe₂. These findings indicate superior carrier transport properties, with a measured mobility of 394.1±38.5 cm²·V⁻¹·s⁻¹ for multilayers. Temperature-dependent ultrafast dynamics, acquired using a custom-built cryogenic pump-probe system, reveal two coherent AP modes, ω₁ and ω₂, with central frequencies of 1.27 and 0.17 THz, respectively. The higher frequency ω₁ mode corresponds to shear mode with a nominal electron-phonon coupling constant λ_ω1 = 2.22. To our knowledge, this study represents a pioneering investigation that employs low-temperature ultrafast spectroscopy to elucidate the AP mode and strong electron-phonon coupling in semimetallic PtSe₂ systems. These findings offer fundamental insights into the semimetallic nature of PtSe₂ and establish a basis for designing ultrafast photonic devices that harness its distinct optoelectronic response.

Keywords

PtSe₂ / thickness-modulated / electron-phonon coupling / ultrafast optical / low-temperature

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Central South University