12 research outputs found
Statistics of Raman-Active Excitations via Masurement of Stokes-Anti-Stokes Correlations
A general fundamental relation connecting the correlation of Stokes and
anti-Stokes modes to the quantum statistical behavior of vibration and pump
modes in Raman-active materials is derived. We show that under certain
conditions this relation can be used to determine the equilibrium number
variance of phonons.Time and temperature ranges for which such conditions can
be satisfied are studied and found to be available in todays' experimental
standards. Furthermore, we examine the results in the presence of multi-mode
pump as well as for the coupling of pump to the many vibration modes and
discuss their validity in these cases.Comment: 12 pages, 1 figure, accepted for publication in Phys.Rev.
Impurity effects in graphene
We study the effects of impurities on the electronic properties of graphene. The tight-binding Hamiltonian with impurities has been diagonalized by a series of canonical transformations to obtain energy dispersions. Impurity effects on energy is observed as a band gap opening in donor type impurities, whereas acceptor type impurities do not create a gap. However the linear dispersions near the Dirac point turn to quadratic form for both types of impurities. Density of states are also calculated analytically
The ground- and first-excited states of magnetopolarons in two-dimensional quantum dots for all coupling strengths
The stability of magnetobipolarons in low-dimensional systems
We investigate the stability condition of large bipolarons confined in a
parabolic potential containing certain parameters and a uniform
magnetic field. The variational wave function is constructed as a product
form of electronic parts, consisting of center of mass and internal motion,
and a part of coherent phonons generated by Lee-Low-Pines transformation
from the vacuum. An analytical expression for the bipolaron energy is found, from which the ground and excited-state energies are obtained numerically
by minimization procedure. The bipolaron stability region is determined by
comparing the bipolaron energy with those of two separate polarons, which is
already calculated within the same approximation. It is shown that the
results obtained for the ground state energy of bipolarons reduce to the
existing works in zero magnetic field. In the presence of a magnetic field,
the stability of bipolarons is examined, for three types of low-dimensional
system, as function of certain parameters, such as the magnetic-field, the
electron-phonon coupling constant, Coulomb repulsion and the confinement
strength. Numerical solutions for the energy levels of the ground and first
excited states are examined as functions of the same parameters
The ground- and first-excited states of magnetopolarons in two-dimensional quantum dots for all coupling strengths
The ground- and first-excited state energies of a magnetopolaron
in a two dimensional parabolic quantum dot are studied within a
variational calculation for all coupling strength. The
Lee-Low-Pines-Huybrecht variational technique that is developed
previously for all coupling strength has been extented for
polarons in a magnetic field. The dependence of the polaronic
correction on the magnetic field and the confinement length is
investigated. The polarization potential and the renormalized
cyclotron masses as a function of electron-phonon coupling
strength and the strength of both confinement potential and
magnetic field are also studied within the same approach
Two-particle Wigner functions in a one-dimensional Calogero-Sutherland potential
We calculate the Wigner distribution function for the
Calogero-Sutherland system which consists of harmonic and
inverse-square interactions. The Wigner distribution function is
separated out into two parts corresponding to the relative and
center-of-mass motions. A general expression for the relative
Wigner function is obtained in terms of the Laguerre polynomials
by introducing a new identity between Hermite and Laguerre
polynomials
Quantum Optics and Solid State Spectroscopy
Possibility of formation of strongly correlated states of the bosonic excitations in solids similar to the squeezed states of photons is considered. The possibility of observation of these states in optical spectroscopy is discussed