The optical response and plasmon coupling between graphene sheets for graphene/polymer multilayer heterostructures with controlled separation were systematically investigated. Anomalous transmission of light was experimentally observed in mid-infrared range. The position of the broad passband in the transmission spectra was observed to red-shift with the increase of the number of layers.
The spin-related phenomena in semiconductor nanostructures are
currently attracting considerable interest due to the novel
physics and the potential application in electronics and
optoelectronics. The Rashba and Dresselhaus spin-orbit
interactions play an important role in controlling and
manipulating the spin and charge degrees of freedom in
low-dimensional and nanoscale semiconductor systems. We present a
study of quantum transport and optical properties in spintronic
materials in the terahertz frequency regime and discuss the
potential application of spintronic materials in terahertz
Conventional solid-state and vacuum thermionic devices restrict the flow of electrons between the hot and cold reservoirs according to the magnitude of their momentum in the direction of transport only. Recently it has been suggested that devices may be developed where the filtering of transmitted electrons occurs according to their total momentum. We compare the performance of these two different methods of electron momentum filtering in single barrier and resonant tunneling thermionic refrigeration devices. It is shown that total momentum filtered single barrier refrigerators always outperform conventional single barrier refrigerators due to their larger heat current which is particularly important when the thermal conductivity of the system is significant. We show that whilst conventionally filtered resonant tunneling thermionic refrigerators are outperformed by total momentum resonant tunneling thermionic refrigerators in many conditions, their performance is superior at (1) high temperatures or (2) when the transmission energy is very close to the Fermi energy.
We consider the effect that the barrier shape has on the electron energy spectrum and lattice thermal conductivity, and together the effect of these coefficient of performance of thermionic refrigerators. Whilst it is shown that wide barriers are also desirable to enhance the electron energy spectrum, the primary motivation to increase barrier width to the maximum allowable value with ballistic transport is to reduce thermal conductivity. It is shown that the barriers which produce the highest electronic coefficient of performance do not necessarily give the highest coefficient of performance when thermal conductivity is considered if electronic heat current is reduced. While mean free path length multibarrier geometries may offer reduced thermal conductivity due to the possibility of interface scattering and phonon miniband formation, this effect needs to be significant to achieve coefficient of performance comparable with a single barrier device. Finally, we show that maximum refrigerator coefficient of performance is achieved by transmitting electrons over a tuned energy range only, which may be approximated by the transmission probability associated with a Gaussian modulated superlattice.
We enunciate the general principles that govern the transport of charge and heat in a thermionic device. We illustrate the application of these principles to the subject of domestic refrigeration. A complementary application is power generation. We distinguish Class 2 devices, in which the potential barrier on the hot side plays a role, from Class 1 devices, in which this barrier is irrelevant. We show that the effect of heat backflow is to drastically reduce the efficiency of thermionic devices in both GaAs and InSb representative semiconductor systems. We conclude that practical devices are not likely with bulk, single-barrier devices.
The quantum transport equation for electrons under intense
radiation was solved. The frequency-dependent electrical current
driven directly by the radiation field is obtained. The electrical
field of the laser radiation is included exactly and the
electron-impurity interaction is included up to the second order.
Our formalism rests on the solution of density matrix for
successive order of photon processes. It is found that as
radiation intensity increases, the rate of multiphoton absorption
and emission can exceed that of single photon processes. In the
strong electron-photon coupling limit, rate of emission is
comparable to that of absorption.
We study the density response function of a semiconductor heterostructure under a quantising magnetic field and a laser
radiation. Under resonant condition of when photon sideband gap equals Landau level separation, a new intra-level plasmon mode emerges. The new mode increases rapidly with the decreasing magnetic field in the low field regime and behaves like a sound wave in the large wavevector regime.
Absorption of electromagnetic waves in electronic systems coupled
to intense terahertz waves is calculated. We formulate a theoretical framework suitable for calculating the frequency-dependent electrical current under an intense THz radiation. This first principle method is based on the time-evolution of electron density matrix and it includes electron-photon coupling to all orders. We first obtained the time-dependent electronic states as a function of terahertz field and frequency. The electron-impurity scattering is included to the second order. The absorption of electromagnetic waves of a probing field via various electron-terahertz-photon coupling is then obtained in terms of frequency-dependent dielectric functions.