Speaker
Description
D. Sekyi-Arthur*, E. Atioyire, K.A. Dompreh, S.Y. Mensah
Department of Physics, University of Ghana
Email: dsekyi-arthur@ug.edu.gh, rasdean3@gmail.com
In this work, we investigate the nonlinear acoustoelectric transport phenomena in fluorine-doped single-walled carbon nanotubes (FSWCNTs) subjected to high-frequency electric fields in the hypersound regime (ql≫1), where q is the acoustic wavenumber and l is the carrier mean free path. Using a semiclassical Boltzmann transport equation under a constant relaxation time approximation, we analyze the acoustoelectric direct current (ADC) response in the presence of a combined DC-AC electric field and longitudinal acoustic phonons.
Our study reveals self-sustaining current oscillations resulting from the interplay between Bloch oscillations, space-charge instabilities, and acoustic phonon scattering. These oscillations manifest in the axial acoustoelectric current density as highly nonlinear and non-monotonic behaviors, particularly under strong electric fields (ωτ ≫ 1, z ≫ 1). We demonstrate that the current exhibits harmonic oscillations, negative differential conductivity (NDC), and even polarity reversal depending on the amplitude of the AC field and material parameters such as the axial and circumferential overlap integrals (∆_z, ∆_s).
Significantly, the acoustoelectric response is highly sensitive to changes in the Bloch frequency (Ωτ), electron-phonon coupling strength, temperature, and doping concentration. We find that at moderate field strengths (e.g., z = 4), Bloch oscillations can exist without triggering significant space charge instability, leading to smooth NDC profiles. However, at higher fields (z = 6 and 8), strong carrier heating and bunching reintroduce space charge waves and lead to large oscillatory currents with reversed polarity.
We provide analytical and numerical solutions to the carrier dynamics, highlighting the role of Bessel function modulation and miniband transport. Theoretical predictions align with experimentally measured acoustoelectric responses in graphene and other low-dimensional systems, supporting the model’s validity.
Our findings suggest that FSWCNTs, due to their tunable electronic properties and high thermal/electrical stability, are excellent candidates for use in THz wave generation, nanoelectronic switches, and acoustic-driven quantum devices. The absence of a required resonator for current oscillation further enhances their practicality in compact and integrated terahertz systems. This work contributes to the broader understanding of high-frequency quantum transport and the engineering of novel materials for advanced optoelectronic applications.
Keywords: Acoustoelectric current, fluorine-doped carbon nanotubes, Bloch oscillations, nonlinear transport, negative differential conductivity, THz generation, hypersound, space charge instabilities.