Phonon modulation of Stark-cyclotron resonances

We demonstrate the possibility of oscillations of magnetic peak positions of the Stark-cyclotron resonance due to acoustic phonon scattering in confined superlattices and investigate oscillations of the hopping current in the Wannier–Stark localization regime due to phonon folding and electron Bragg reflection. Manifestation of these effects in recent experiments is discussed.     

Nonlinear transport and heat dissipation in metallic carbon nanotubes

We show that the local temperature dependence of thermalized electron and phonon populations along metallic carbon nanotubes is the main reason behind the nonlinear transport characteristics in the high bias regime. Our model is based on the solution of the Boltzmann transport equation considering both optical and zone boundary phonon emission as well as absorption by charge carriers. It also assumes a local temperature along the nanotube, determined self-consistently with the heat transport equation. By using realistic transport parameters, our results not only reproduce experimental data for electronic transport but also provide a coherent interpretation of thermal breakdown under electric stress. In particular, electron and phonon thermalization prohibits ballistic transport in short nanotubes.     

Energy diffusion equation for an electron gas interacting with polar optical phonons: Non-parabolic case

A novel method previously presented to explicitly solve the Boltzmann equation for highly energetic electrons interacting with polar optical phonons is improved in order to take into account the non-parabolicity of the conduction band. For the case of field free spatial diffusion, the carrier velocity is compared with Monte Carlo simulations. For GaAs the agreement between the analytical and the numerical method is quite good at 77 and 300 K. Also, the results derived for a parabolic band structure show a strong overestimation of the carrier velocity.     

General model of the transverse dielectric constant of GaAs-AlAs superlattices

A general model of the transverse dielectric constant of GaAs-AlAs superlattices is presented. The model is based on treating separately the individual contributions from the Λ, X, and L valleys, enabling us to understand better the general trends of the overall dielectric constant. An accurate · band calculation is used to determine the bulk band structure around the three symmetry points and a realistic Kronig-Penney model is used to calculate the influence of the superlattice periodicity on the bulk band structure. The resulting dielectric constant shows a small polarization effect due to the anisotropy of the superstructure and a large amount of fine structure corresponding to different transitions between the quantized levels. The influence of the barrier and well thicknesses, L_B and L_Z, respectively, is also important and it is shown that for a constant value of =L_B/(L_B+L_Z), the real part of the zero frequency dielectric constant increases as a function of L_B. Finally, the real parts of the dielectric constants of a superlattice and the corresponding AlGaAs alloy, characterized by the same value of , are compared and it is found that at zero frequency the superlattice dielectric constant is slightly larger with the difference increasing for higher frequencies.     

Effect of magnetic domains on the electrical resistivity of a ferromagnet just below the critical temperature

The motion of magnetic domains has been detected by measurements of the electrical resistivity temperature derivative in the vicinity of the critical temperature of various ferromagnetic systems. The case of TbZn serves as an illustration. A theoretical model is based on a mean field expression for the electrical resistivity.     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.