In macroscopic bulk systems, current noise is regarded merely as an undesirable disturbance. However, in low-dimensional and nanoscale materials, it serves as a powerful probe to analyze microscopic scattering processes occurring within the material. Specifically, current noise arising from phonons (thermal atomic vibrations) reflects the details of electron–phonon interactions, energy dissipation, and nonequilibrium dynamics, making it an important topic in condensed matter physics.

In this study, we focus on the fact that current noise, which is typically negligible in bulk materials, becomes pronounced in one-dimensional nanomaterials such as carbon nanotubes (CNTs). We demonstrate theoretically that the high-frequency components of current noise encode new information about complex electron–phonon scattering processes within the material.

We conduct a detailed analysis of the frequency dependence of phonon-induced current noise in armchair single-walled carbon nanotubes. Our approach combines atomistic quantum transport simulations, based on the time-dependent Schrödinger equation for open systems (open TDSE), with molecular dynamics simulations. In the low-frequency regime (ω ≪ ω_c), where ω_c (~3 rad/ps) is the characteristic frequency determined by the correlation time τ_c of current fluctuations due to phonon scattering, the power spectral density follows a Lorentzian form predicted by a Markov model in which electrons propagate while being randomly scattered by phonons.

In contrast, in the high-frequency regime (ω ≫ ω_c), multiple resonance peaks emerge that deviate from the Lorentzian shape. Our analysis reveals that several of these peaks correspond to electron scattering by specific phonon modes characteristic of CNTs, including the radial breathing mode (RBM), radial breathing-like mode (RBLM), and out-of-plane transverse optical mode (oTO). Remarkably, however, a peak observed at ~89 rad/ps could not be explained by conventional harmonic phonon scattering. Detailed investigation suggests that this peak originates from anharmonic phonon effects—specifically, four-phonon processes involving the simultaneous participation of multiple phonons. Identifying such nontrivial sources of noise highlights electron–phonon interactions complexity and provides a new perspective beyond conventional theoretical frameworks.

These findings also have significant implications for future applications. Recent advances in terahertz-frequency noise spectroscopy have facilitated the experimental testing of these theoretical predictions using CNT-based systems. If performed, such experiments would provide valuable insights into the design of ultrafast, low-power quantum devices. In summary, our results elucidate the fundamental nature of electron–phonon interactions and noise phenomena in one-dimensional nanomaterials. Moreover, this work lays a foundation for the development of next-generation electronic technologies.

(Written by Takahiro Yamamoto on behalf of all authors.)

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