Conditions for the Emergence of Spontaneous Phonon Frequency Combs from Anharmonic Potentials
Abstract
Phononic frequency combs have been demonstrated experimentally and theoretically in the kHz-MHz regime under nonlinear driving; however, their spontaneous formation in the GHz-THz regime remains rare. We investigate the spontaneous formation of frequency combs in van der Waals solid CrGeTe3, where combs of spacing ∼2 cm−1 were experimentally proposed to occur in a flat phonon mode but are now reported to originate from isotopic distribution. Our spectral energy density calculations using machine-learning-augmented molecular dynamics simulations show comb-like features with reduced spacings of ∼0.1 and 0.6 cm−1 in the same mode at 50 and 200 K. However, the spacings of the comb-like features are comparable to the phonon linewidth, making precise identification of the frequency comb challenging. From a comprehensive analysis of different modes of CrGeTe3, we identified two conditions to distinctively observe the combs beyond the experimental resolution: (i) an intramolecular or isolated mode with reasonably large third- or higher-order anharmonicity from phonon self-interaction and (ii) limited phonon scattering channels. Our analysis of other van der Waals solids highlighted that these conditions are met for the nearly flat intramolecular E2g and A2u phonon modes of WSe2. The detailed calculations showed the formation of a spontaneous frequency comb with spacings of 1.7 and 0.67 cm−1 from coherent superposition of four and five-phonon eigenstates in the E2g and A2u phonon modes, respectively. Available Raman scattering data of the E2g mode in the literature provide preliminary, if not conclusive, evidence of comb formation. Our findings offer a deeper understanding and open avenues for engineering long-lived phononic frequency combs for various practical applications.
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BibTeX
@misc{jayakrishnan2026conditions,
title = {{Conditions for the Emergence of Spontaneous Phonon Frequency Combs from Anharmonic Potentials}},
author = {Jayakrishnan SS and Mayanak K Gupta and Dipanshu Bansal},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.17707},
eprint = {2609.17707},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.17707},
}
RIS
TY - UNPB
TI - Conditions for the Emergence of Spontaneous Phonon Frequency Combs from Anharmonic Potentials
AU - Jayakrishnan SS
AU - Mayanak K Gupta
AU - Dipanshu Bansal
PY - 2026
DA - 2026/09/15
PB - arXiv
DO - 10.48550/arxiv.2609.17707
UR - https://arxiv.org/abs/2609.17707
AB - Phononic frequency combs have been demonstrated experimentally and theoretically in the kHz-MHz regime under nonlinear driving; however, their spontaneous formation in the GHz-THz regime remains rare. We investigate the spontaneous formation of frequency combs in van der Waals solid CrGeTe_3, where combs of spacing ∼2 cm^−1 were experimentally proposed to occur in a flat phonon mode but are now reported to originate from isotopic distribution. Our spectral energy density calculations using machine-learning-augmented molecular dynamics simulations show comb-like features with reduced spacings of ∼0.1 and 0.6 cm^−1 in the same mode at 50 and 200 K. However, the spacings of the comb-like features are comparable to the phonon linewidth, making precise identification of the frequency comb challenging. From a comprehensive analysis of different modes of CrGeTe_3, we identified two conditions to distinctively observe the combs beyond the experimental resolution: (i) an intramolecular or isolated mode with reasonably large third- or higher-order anharmonicity from phonon self-interaction and (ii) limited phonon scattering channels. Our analysis of other van der Waals solids highlighted that these conditions are met for the nearly flat intramolecular E_2g and A_2u phonon modes of WSe_2. The detailed calculations showed the formation of a spontaneous frequency comb with spacings of 1.7 and 0.67 cm^−1 from coherent superposition of four and five-phonon eigenstates in the E_2g and A_2u phonon modes, respectively. Available Raman scattering data of the E_2g mode in the literature provide preliminary, if not conclusive, evidence of comb formation. Our findings offer a deeper understanding and open avenues for engineering long-lived phononic frequency combs for various practical applications.
ER -