38 research outputs found
Contribution of One-Time Pair Correlation Function to Kinetic Phenomena in Nonequilibrium Gas
It has been established in nineteen seventies that in nonequilibrium case the
pair collisions generate non-zero two-particle correlations which are
non-diagonal in momentum space and give the essential contribution to the
current fluctuations of hot electrons. It is shown here that this correlations
give also a contribution to the collision integral, i.e., to kinetic properties
of nonequilibrium gas. The expression for electron energy loss rate P via
phonons is re-derived in detail from this point of view. The contribution of
the non-diagonal part of the nonequilibrium pair correlator to phonon-electron
collision integral and to P is obtained and explicitly calculated in the
electron temperature approximation. It is shown that these results can be
obtained from stochastic non-linear kinetic equation with Langevin fluctuation
force. Such an approach allows to formulate the simple general conditions under
that a contribution of two-particle correlations might be essential in
kinetics. The contribution obtained does not contain the extra powers of small
gas parameter unlike the equilibrium virial decompositions.Comment: 6 pages, based on the report presented at the conference ``Progress
in Nonequilibrium Green's Functions'', Dresden, Germany, 19.-22. August 200
Genuine converging solution of self-consistent field equations for extended many-electron systems
Calculations of the ground state of inhomogeneous many-electron systems
involve a solving of the Poisson equation for Coulomb potential and the
Schroedinger equation for single-particle orbitals. Due to nonlinearity and
complexity this set of equations, one believes in the iterative method for the
solution that should consist in consecutive improvement of the potential and
the electron density until the self-consistency is attained. Though this
approach exists for a long time there are two grave problems accompanying its
implementation to infinitely extended systems. The first of them is related
with the Poisson equation and lies in possible incompatibility of the boundary
conditions for the potential with the electron density distribution. The
analysis of this difficulty and suggested resolution are presented for both
infinite conducting systems in jellium approximation and periodic solids. It
provides the existence of self-consistent solution for the potential at every
iteration step due to realization of a screening effect. The second problem
results from the existence of continuous spectrum of Hamiltonian eigenvalues
for unbounded systems. It needs to have a definition of Hilbert space basis
with eigenfunctions of continuous spectrum as elements, which would be
convenient in numerical applications. The definition of scalar product
specifying the Hilbert space is proposed that incorporates a limiting
transition. It provides self-adjointness of Hamiltonian and, respectively, the
orthogonality of eigenfunctions corresponding to the different eigenvalues. In
addition, it allows to normalize them effectively to delta-function and to
prove in the general case the orthogonality of the 'right' and 'left'
eigenfunctions belonging to twofold degenerate eigenvalues.Comment: 12 pages. Reported on Interdisciplinary Workshop "Nonequilibrium
Green's Functions III", August 22 - 26, 2005, University Kiel, Germany. To be
published in Journal of Physics: Conference Series, 2006; Typos in Eqs. (37),
(53) and (54) are corrected. The content of the footnote is changed.
Published version available free online at
http://www.iop.org/EJ/abstract/1742-6596/35/1/01
Observation of anomalously strong penetration of terahertz electric field through terahertz-opaque gold films into a GaAs/AlGaAs quantum well
We observe an anomalously high electric field of terahertz (THz) radiation
acting on a two-dimensional electron gas (2DEG) placed beneath a thin gold
film, which, however, is supposed to be opaque at THz frequencies. We show that
the anomalously strong penetration of the THz electric field through a very
high conductive gold film emerges if two conditions are fulfilled
simultaneously: (i) the film's thickness is less than the skin depth and (ii)
the THz electric field is measured beneath the film at distances substantially
smaller than the radiation wavelength. We demonstrate that under these
conditions the strength of the field acting on a 2DEG is almost the same as it
would be in the absence of the gold film. The effect is detected for
macroscopically homogeneous perforation-free gold films illuminated by
THz-laser radiation with a spot smaller than the film area. This eliminates the
near-field of the edge diffraction as a possible cause of the anomalous
penetration. The microscopic origin of the effect remains unexplained in its
details, yet. The observed effect can be used for the development of THz
devices based on two-dimensional materials requiring robust highly conducting
top gates placed at less than nanometer distance from the electron gas
location