We investigated several proposals utilizing the unique electronic properties of carbon nanotubes (CNTs) for a broad range of applications to THz optoelectronics, including THz generation by Cerenkov-type emitters based on carbon nanotubes and by hot electrons in quasimetallic 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. Dispersion equations of the electron beam instability and the threshold conditions of the stimulated emission have been derived and analyzed, demonstrating realizability of the nanotube-based nanoFEL at realistic parameters of nanotubes and electronic beams.
We propose a new strategy for ultrafast magnetization reversal of nanomagnets. Due to the Inverse Faraday Effect, circularly polarized optical pulses induce a pulsed magnetic flux in materials with large magneto-optical susceptibility. Alternatively, intense optical pulses can induce a pulsed magnetic flux by means of ultrafast demagnetization of a metallic thin film or multilayer with a perpendicular magnetic anisotropy. The time varying magnetic flux induces a transient electro-motive force and electric current in a conducting loop on the surface of the illuminated material, and hence a transient magnetic field. The magnetic field pulses due to the transient current appear to be too short for use in the magnetic field or spin-current induced precessional switching of magnetization. However, our calculations suggest that the magnetic field could lead to ultrafast switching of a nanomagnet overlaid on the surface of the conductor and demagnetized by the same optical pulse. In the case of magnetic pulses due to the Inverse Faraday Effect, the switching direction could be controlled by the helicity of the optical pulse.
In a material with large magneto-optical susceptibility, due to the Inverse Faraday Effect, circularly polarized optical
pulses induce a pulsed magnetic flux. Alternatively, sufficiently intense optical pulses can induce a pulsed magnetic flux
by means of ultrafast demagnetization of a metallic thin film or multilayer with a perpendicular magnetic anisotropy.
The time varying magnetic flux may induce a transient electro-motive force and electric current in a conducting loop on
the surface of the illuminated material. The latter current induces a transient magnetic field that can be used in various
nanomagnetic processes. The magnetic field pulses due to the transient current appear to be too short for use in the
magnetic field or spin-current induced precessional switching of magnetization. However, our calculations suggest that
the magnetic field could lead to ultrafast switching of a nanomagnet overlaid on the surface of the conductor and
demagnetized by the same optical pulse. In the case of photo-magnetic pulses due to the Inverse Faraday Effect, the
switching direction could be controlled by the helicity of the optical pulse. We also demonstrate that the proposed
device, which we call a Faraday Magneto-Optical Transformer, could be used as a Terahertz emitter.
We formulate and justify several proposals utilizing the unique electronic properties of different types of carbon
nanotubes in 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 by armchair nanotubes in strong magnetic fields.
We study an electron-hole system in double quantum wells theoretically using the powerful Green's function technique. We demonstrate that there is a temperature interval over which an abrupt jump in the value of the ionization degree occurs with an increase of the carrier density or temperature. The opposite effect, the collapse of the ionized electron-hole plasma into an insulating exciton system, should occur at lower densities. In addition, we predict that under certain conditions there will be a sharp decrease of the ionization degree with increasing temperature-the anomalous Mott transition. We discuss how these effects could be observed experimentally.
Electron motion in an (n,1) carbon nanotube is shown to correspond to a de Broglie wave propagating along a helical line on the nanotube wall. This helical motion leads to periodicity of the electron potential energy in the presence of an electric field normal to the nanotube axis. The period of this potential is proportional to the nanotube radius and is greater than the interatomic distance in the nanotube. As a result, the behavior of an electron in an (n,1) nanotube subject to a transverse electric field is similar to that in a semiconductor superlattice. In particular, Bragg scattering of electrons from the long-range periodic potential results in the opening of gaps in the energy spectrum of the nanotube. Modification of the bandstructure is shown to be significant for experimentally
attainable electric fields, which raises the possibility of applying this effect to novel nanoelectronic devices.
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