6 research outputs found
Second Harmonic Generation in Gapped Graphene
The second-order nonlinear optical susceptibility for second
harmonic generation is calculated for gapped graphene. The linear and
second-order nonlinear plasmon excitations are investigated in context of
second harmonic generation (SHG). We report a red shift and an order of
magnitude enhancement of the SHG resonance with growing gap, or alternatively,
reduced electro-chemical potential.Comment: 10 pages,10 figure
Spin-dependent Scattering by a Potential Barrier on a Nanotube
The electron spin effects on the surface of a nanotube have been considered
through the spin-orbit interaction (SOI), arising from the electron confinement
on the surface of the nanotube. This is of the same nature as the
Rashba-Bychkov SOI at a semiconductor heterojunction. We estimate the effect of
disorder within a potential barrier on the transmission probability. Using a
continuum model, we obtained analytic expressions for the spin-split energy
bands for electrons on the surface of nanotubes in the presence of SOI. First
we calculate analytically the scattering amplitudes from a potential barrier
located around the axis of the nanotube into spin-dependent states. The effect
of disorder on the scattering process is included phenomenologically and
induces a reduction in the transition probability. We analyzed the relative
role of SOI and disorder on the transmission probability which depends on the
angular and linear momentum of the incoming particle, and its spin orientation.
We demonstrated that in the presence of disorder perfect transmission may not
be achieved for finite barrier heights.Comment: 16 pages, 15 figure
Quantum ballistic transport by interacting two-electron states in quasi-one-dimensional channels
For quantum ballistic transport of electrons through a short conduction channel, the role of Coulomb interaction may significantly modify the energy levels of two-electron states at low temperatures as the channel becomes wide. In this regime, the Coulomb effect on the two-electron states is calculated and found to lead to four split energy levels, including two anticrossing-level and two crossing-level states. Moreover, due to the interplay of anticrossing and crossing effects, our calculations reveal that the ground two-electron state will switch from one anticrossing state (strong confinement) to a crossing state (intermediate confinement) as the channel width gradually increases and then back to the original anticrossing state (weak confinement) as the channel width becomes larger than a threshold value. This switching behavior leaves a footprint in the ballistic conductance as well as in the diffusion thermoelectric power of electrons. Such a switching is related to the triple spin degeneracy as well as to the Coulomb repulsion in the central region of the channel, which separates two electrons away and pushes them to different channel edges. The conductance reoccurrence region expands from the weak to the intermediate confinement regime with increasing electron density
Finite-temperature plasmons, damping and collective behavior for model
We have conducted a thorough theoretical and numerical investigation of the
electronic susceptibility, polarizability, plasmons, their damping rates, as
well as the static screening in pseudospin-1 Dirac cone materials with a flat
band, or for a general model, at finite temperatures.
This includes calculating the polarization function, plasmon dispersions and
their damping rates at arbitrary temperatures and obtaining analytical
approximations the long wavelength limit, low and high temperatures. We
demonstrate that the integral transformation of the polarization function
cannot be used directly for a dice lattice revealing some fundamental
properties and important applicability limits of the flat band dispersions
model. At , the largest temperature-induced change of the
polarization function and plasmons comes from the mismatch between the chemical
potential and the Fermi energy. We have also obtained a series of closed-form
semi-analytical expressions for the static limit of the polarization function
of an arbitrary material at any temperature with exact
analytical formulas for the high, low and zero temperature limits which is of
tremendous importance for all types of transport and screening calculations for
the flat band Dirac materials.Comment: 19 pages, 8 figure