Nam Lyong Kang

Derivation of linewidths for optical transitions in quantum wells due to longitudinal optical phonon scattering

Utilizing the quantum statistical operator algebra technique, we derive a new absorption coefficient formula for the optical transition in a system of electrons interacting with longitudinal optical phonons in a quantum well. The electron and phonon distribution functions are included in the lineshape function. So we can explain the phonon absorptions and emissions in an organized way for all the electron transition processes. The numerical results show that the width decreases with the well width and increases with the temperature.

Magnetic field dependence of cyclotron resonance linewidths in Ge and Si by a projection technique

The magnetic field dependence of cyclotron resonance linewidths is examined theoretically on the basis of the projection technique. It is shown that in the quantum limit of pure Ge and Si the widths increase with the magnetic field, and the result for Ge agrees quite well with the existing experimental data.

A Simple Projection Approach to Cyclotron Absorption Linewidths Due to Piezoelectric Phonon Scattering

The temperature and magnetic field dependences of cyclotron resonance linewidths in the quantum limit due to piezoelectric phonon scattering in CdS, ZnS and GaAs are examined theoretically by a simple projection approach. We find that the width increases with the temperature, but decreases as the magnetic field increases for all the materials. It is shown that the result for the temperature dependence of the width in CdS is in good agreement with the experimental result of Kobori et al.

Projection-Reduction Approach to Optical Conductivities for an Electron-Phonon System and Their Diagram Representation

Utilizing state-dependent projection operators and the Kang-Choi reduction identities, we derive the linear, first, and second-order nonlinear optical conductivities for an electron system interacting with phonons. The lineshape functions included in the conductivity tensors satisfy “the population criterion” saying that the Fermi distribution functions for electrons and Planck distribution functions for phonons should be combined in multiplicative forms. The results also contain energy denominator factors enforcing the energy conservation as well as interaction factors describing electron-phonon interaction properly. Therefore, the phonon absorption and emission processes as well as photon absorption and emission processes in all electron transition processes can be presented in an organized manner and the results can be represented in diagrams that can model the quantum dynamics of electrons in a solid.

Cyclotron-transition linewidths in Ge with anisotropic scattering

Utilizing the state-independent projection technique, we obtain a general formula for the cyclotron-transition linewidth for anisotropic deformation potential phonon scattering. The formula is applied to calculate the width in Ge at low temperatures. It is shown that the transition between the two lowest adjacent Landau levels makes the most contribution to the temperature and the magnetic field dependence of the width, and the result agrees better with the experiment as the higher-order contributions are included. The width increases with the magnetic field, implying that the interaction of electrons with acoustic phonons increases with the field.

Theory of conductivity in a quasi-two-dimensional system based on operator algebra technique

We describe a method of obtaining a conductivity formula which incorporates the relaxation functions in a quasi-two-dimensional system. A parabolic confinement potential is adopted. We derive the relaxation function using projectors. We expand the propagators via the series expansion of the diagonal projectors and obtain useful relations enabling one to calculate the relaxation functions.

Comparison of four scattering mechanisms in cyclotron resonance in InSb

SummaryFour scattering mechanisms are compared in the quantum limit cyclotron resonance inn-InSb on the basis of a many body theory introduced recently. In the quite low temperature region (T<70 K ) for the wavelength of the electromagnetic wave of 84 μ m, the electrons are scattered mostly by the ionized impurities, although the deformation potential phonon and the piezoelectric scattering are non-negligible. In the high temperature region (T>70 K ) the polar optical phonon scattering is found to be most dominant. It is also shown that the impurities give place to the phonons for the scattering mechanism above 70 K. On the other hand, at 20 K the ionized impurity scattering is dominant in the magnetic field region 0.2 T