Torsional oscillation of carbon nanotubes driven by electron spins

Abstract

We theoretically investigate the current-induced excitation of torsional vibrations in a suspended carbon nanotube (CNT) quantum dot. By considering a CNT clamped between half-metallic ferromagnetic electrodes with an antiparallel magnetization configuration, we demonstrate that the spin-rotation coupling enables the transfer of angular momentum from electron spins to the mechanical torsional mode under a constant source-drain voltage. Using a master-equation approach to analyze the coupled dynamics of the dot levels and a quantized torsional oscillator, we evaluate the steady-state current and phonon distribution. We find that when the Zeeman splitting matches the torsional phonon energy, the system exhibits a sharp resonant behavior in the current, accompanied by a significant increase in the phonon population. Our estimates for realistic device parameters indicate that this spin-driven mechanism can drive CNT torsional vibrations with detectable amplitudes. This work provides a theoretical basis for current-controlled actuation of nanoelectromechanical systems via the spin angular momentum of electrons.

Figures (7)

• Figure 1: Schematic illustration of the model: A suspended CNT of length $L$ is connected to half-metallic ferromagnetic electrodes magnetized along opposite directions.
• Figure 2: Energy-level diagram of the CNT quantum dot.
• Figure 3: Contour plot of the current as a function of $\hbar\omega_0$ and $h$. The parameters are set as $k_{\rm B}T = 2.0\, \mu\mathrm{eV} = 23.2\, \mathrm{mK}$, $\mu_{\mathrm{L}} = -\mu_{\mathrm{R}} = 150\, \mu\mathrm{eV}$, and $k_\mathrm{relax} = 3.0\times10^{-5}\omega_0$.
• Figure 4: Probability distributions of the CNT torsional mode. The parameters are set as $h=\hbar\omega_0 = 250\, \mu\mathrm{eV}$, $k_{\mathrm{B}}T = 2.0\, \mu\mathrm{eV} = 23.2\, \mathrm{mK}$, $\mu_{\mathrm{L}} = -\mu_{\mathrm{R}} = 150\, \mu\mathrm{eV}$, and $k_\mathrm{relax} = 3.0\times10^{-5}\omega_0$.
• Figure 5: Contour plot of the current as a function of $\mu_{\mathrm{L}}$ and $\mu_{\mathrm{R}}$. The parameters are set as $h = \hbar\omega_0 = 200\, \mu\mathrm{eV}$, $k_{\mathrm{B}} T = 10.0\, \mu\mathrm{eV} = 116\, \mathrm{mK}$, and $k_\mathrm{relax} = 3.0\times10^{-5}\omega_0$.