Journal Article

Spontaneously formed phonon frequency combs in van der Waals solid CrGeTe3 and CrSiTe3

He, Rui, Chen, Lebing, Birgeneau, Robert J., Nnokwe, Cynthia, Tanigaki, Katsumi, Pan, Xing-Chen, Cheng, Guanghui, Llacsahuanga Allcca, Andres E., Chen, Yong P., Mandrus, David G., Ye, Gaihua, Giles-Donovan, Nathan, Yan, Jiaqiang

2025

Overview

Optical phonon engineering through nonlinear effects has been utilized in ultrafast control of material properties. However, nonlinear optical phonons typically exhibit rapid decay due to strong mode-mode couplings, limiting their effectiveness in temperature or frequency sensitive applications. Here we report the observation of long-lived nonlinear optical phonons through the spontaneous formation of phonon frequency combs in the van der Waals material CrXTe 3 (X=Ge, Si) using high-resolution Raman scattering. Unlike conventional optical phonons, the highest A g mode in CrGeTe 3 splits into equidistant, sharp peaks forming a frequency comb that persists for hundreds of oscillations and survives up to 200K. These modes correspond to localized oscillations of Ge 2 Te 6 clusters, isolated from Cr hexagons, behaving as independent quantum oscillators. Introducing a cubic nonlinear term to the harmonic oscillator model, we simulate the phonon time evolution and successfully replicate the observed comb structure. Similar frequency comb behavior is observed in CrSiTe 3 , demonstrating the generalizability of this phenomenon. Our findings demonstrate that Raman scattering effectively probes high-frequency nonlinear phonon modes, offering insight into the generation of long-lived, tunable phonon frequency combs with potential applications in ultrafast material control and phonon-based technologies. Nonlinear optical phonons often exhibit rapid decay. Here, the authors demonstrate long-lived nonlinear optical phonons through the spontaneous formation of phonon frequency combs in CrXTe 3 (X=Ge,Si).

• Publisher: Nature Publishing Group UK,Nature Publishing Group,Nature Portfolio
• Subject: 639/624/1107/527/1821 / 639/624/1111/1112 / 639/624/400/385 / Couplings / Decay / Electrons / Energy / Experiments / frequency combs / Germanium / Harmonic oscillators / Hexagons / Humanities and Social Sciences / Magnetic fields / Material properties / multidisciplinary / Nonlinear optics / Optical properties / Oscillations / Oscillators / Phonons / Raman spectra / raman spectroscopy / Science / Science (multidisciplinary) / Silicon / Spectrum analysis / Temperature