Intersubband plasmons in the quantum limit in gated and aligned carbon nanotubes

Abstract

Confined electrons collectively oscillate in response to light, resulting in a plasmon resonance whose frequency is determined by the electron density and the size and shape of the confinement structure. Plasmons in metallic particles typically occur in the classical regime where the characteristic quantum level spacing is negligibly small compared to the plasma frequency. In doped semiconductor quantum wells, quantum plasmon excitations can be observed, where the quantization energy exceeds the plasma frequency. Such intersubband plasmons occur in the mid- and far-infrared ranges and exhibit a variety of dynamic many-body effects. Here, we report the observation of intersubband plasmons in carbon nanotubes, where both the quantization and plasma frequencies are larger than those of typical quantum wells by three orders of magnitude. As a result, we observed a pronounced absorption peak in the near-infrared. Specifically, we observed the near-infrared plasmon peak in gated films of aligned single-wall carbon nanotubes only for probe light polarized perpendicular to the nanotube axis and only when carriers are present either in the conduction or valence band. Both the intensity and frequency of the peak were found to increase with the carrier density, consistent with the plasmonic nature of the resonance. Our observation of gate-controlled quantum plasmons in aligned carbon nanotubes will not only pave the way for the development of carbon-based near-infrared optoelectronic devices but also allow us to study the collective dynamic response of interacting electrons in one dimension.

Intersubband plasmon excitations in doped carbon nanotubes

“…Senga et al showed consistent absorption peaks for isolated metallic SWNTs that are unintendedly doped on the TEM supporting grid during electron * daria.satco@skoltech.ru † nugraha@flex.phys.tohoku.ac.jp energy-loss spectroscopy (EELS) measurement [22,23]. Yanagi et al proposed that the absorption peaks are related with intersubband plasmon excitations [21], i.e., the optical transitions with energies E ij occur collectively between two electronic subbands i and j as a response to the perpendicularly polarized light. Unlike the interband excitations E ii which take place from the valence to the conduction bands, the intersubband plasmon excitations E ij occur within the conduction band or within the valence band.…”

Isotropic Seebeck coefficient of aligned single-wall carbon nanotube films

“…We employed the recently reported controlled vacuum filtration method 13 to fabricate wafer-scale singledomain thin films of aligned SWCNTs. By using the electrolyte gating method, 4,12,14 we systematically varied the E F of the SWCNT thin film in a wide range, observing a sign change in S when the system goes from the p-type region to the n-type region. The value of r showed strong in-plane anisotropy, i.e., more conducting in the direction parallel to a)…”

Observation of Intersubband Polaritons in a Single Nanoantenna Using Nano-FTIR Spectroscopy

“…We anticipate that this near-field approach will also enable explorations of strong and ultrastrong light-matter coupling in the single nanoantenna regime for other excitations. 44,45 This approach also holds a great potential for probing nano-scale quantum systems positioned not only on the surface, [25][26][27]35 but also buried within a depth of over one hundred nanometers. For example, a small non-resonant nanoantenna may extend the reach of s-SNOM deeper below the surface and enable spectroscopy of ISB transitions in QWs without strong coupling.…”