We formulate and justify several proposals utilizing unique electronic properties of carbon nanotubes for a broad range of applications to THz optoelectronics, including THz generation by hot electrons in quasi-metallic nanotubes, frequency multiplication in chiral-nanotube-based superlattices controlled by a transverse electric field, and THz radiation detection and emission by armchair nanotubes in a strong magnetic field. c 2007 Elsevier Ltd. All rights reserved.
Keywords: Carbon nanotubes; Terahertz radiationCreating a compact reliable source of terahertz (THz) radiation is one of the most formidable tasks of contemporary applied physics [1]. One of the latest trends in THz technology [2] is to use carbon nanotubes -cylindrical molecules with nanometer diameter and micrometer length [3-5] -as building blocks of novel high-frequency devices. There are several promising proposals of using carbon nanotubes for THz applications including a nanoklystron utilizing extremely efficient high-field electron emission from nanotubes [2,6,7], devices based on negative differential conductivity in large-diameter semiconducting nanotubes [8,9], high-frequency resonant-tunneling diodes [10] and Schottky diodes [11][12][13][14] [20].In this paper we formulate and discuss several novel schemes to utilize the physical properties of single-wall carbon nanotubes (SWNTs) for generation and detection of THz radiation.
The damped harmonic oscillator is a workhorse for the study of dissipation in quantum mechanics. However, despite its simplicity, this system has given rise to some approximations whose validity and relation to more refined descriptions deserve a thorough investigation. In this work, we apply a method that allows us to diagonalize exactly the dissipative Hamiltonians that are frequently adopted in the literature. Using this method we derive the conditions of validity of the rotating-wave approximation (RWA) and show how this approximate description relates to more general ones. We also show that the existence of dissipative coherent states is intimately related to the RWA. Finally, through the evaluation of the dynamics of the damped oscillator, we notice an important property of the dissipative model that has not been properly accounted for in previous works; namely, the necessity of new constraints to the application of the factorizable initial conditions.
We demonstrate theoretically that quasi-metallic carbon nanotubes emit terahertz radiation induced by an applied voltage. It is shown that in the ballistic transport regime their spontaneous emission spectra have a universal frequency and bias voltage dependence, which raises the possibility of utilizing this effect for high-frequency nanoelectronic devices.
We show that an experimentally attainable magnetic field applied along the axis of a metallic carbon nanotube not only opens the gap in the nanotube energy spectrum but also allows optical transitions, which are forbidden in the absence of the field. Possible terahertz applications of this effect are discussed.
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