408 research outputs found
Violation of the Luttinger sum rule within the Hubbard model on a triangular lattice
The frequency-moment expansion method is developed to analyze the validity of
the Luttinger sum rule within the Mott-Hubbard insulator, as represented by the
generalized Hubbard model at half filling and large . For the particular
case of the Hubbard model with nearest-neighbor hopping on a triangular lattice
lacking the particle-hole symmetry results reveal substantial violation of the
sum rule.Comment: 4 pages, 2 figure
Charged mobile complexes in magnetic fields: A novel selection rule for magneto-optical transitions
The implications of magnetic translations for internal optical transitions of
charged mobile electron-hole (--) complexes and ions in a uniform
magnetic field are discussed. It is shown that transitions of such
complexes are governed by a novel exact selection rule. Internal intraband
transitions of two-dimensional (2D) charged excitons in strong magnetic
fields are considered as an illustrative example.Comment: 4 pages, 2 figure
Photoexcited transients in disordered semiconductors: Quantum coherence at very short to intermediate times
We study theoretically electron transients in semiconductor alloys excited by
light pulses shorter than 100 femtoseconds and tuned above the absorption edge
during and shortly after the pulse, when disorder scattering is dominant.
We use non-equilibrium Green functions employing the field-dependent
self-consistent Born approximation. The propagators and the particle
correlation function are obtained by a direct numerical solution of the Dyson
equations in differential form. For the purely elastic scattering in our model
system the solution procedures for the retarded propagator and for the
correlation function can be decoupled.The propagator is used as an input in
calculating the correlation function. Numerical results combined with a
cumulant expansion permit to separate in a consistent fashion the dark and the
induced parts of the self-energy. The dark behavior reduces to propagation of
strongly damped quasi-particles; the field induced self-energy leads to an
additional time non-local coherence. The particle correlation function is
formed by a coherent transient and an incoherent back-scattered component. The
particle number is conserved only if the field induced coherence is fully
incorporated. The transient polarization and the energy balance are also
obtained and interpreted.Comment: Accepted for publication in Phys. Rev. B; 37 pages,17 figure
A Solvable Model of Interacting Fermions in Two Dimensions
We introduce and study an exactly solvable model of several species of
fermions in which particles interact pairwise through a mutual magnetic field;
the interaction operates only between particles belonging to different species.
After an unitary transformation, the model reduces to one in which each
particle sees a magnetic field which depends on the total numbers of particles
of all the other species; this may be viewed as the mean-field model for a
class of anyonic theories. Our model is invariant under charge conjugation C
and the product PT (parity and time reversal). For the special case of two
species, we examine various properties of this system, such as the Hall
conductivity, the wave function overlap arising from the transfer of one
particle from one species to another, and the one-particle off-diagonal density
matrix. Our model is a generalization of a recently introduced solvable model
in one dimension.Comment: Revtex, 7 page
Spinon-Holon Attraction in the Supersymmetric t-J Model with 1/r^2-Interaction
We derive the coordinate representation of the one-spinon one-holon
wavefunction for the supersymmetric model with -interaction. This
result allows us to show that spinon and holon attract each other at short
distance. The attraction gets stronger as the size of the system is increased
and, in the thermodynamic limit, it is responsible for the square root
singularity in the hole spectral function.Comment: 4 pages, 1 .eps figur
Localized Wavefunctions and Magnetic Band Structure for Lateral Semiconductor Superlattices
In this paper we present calculations on the electronic band structure of a
two-dimensional lateral superlattice subject to a perpendicular magnetic field
by employing a projection operator technique based on the ray-group of
magnetotranslation operators. We construct a new basis of appropriately
symmetrized Bloch-like wavefunctions as linear combination of well-localized
magnetic-Wannier functions. The magnetic field was consistently included in the
Wannier functions defined in terms of free-electron eigenfunctions in the
presence of external magnetic field in the symmetric gauge. Using the above
basis, we calculate the magnetic energy spectrum of electrons in a lateral
superlattice with bi-directional weak electrostatic modulation. Both a square
lattice and a triangular one are considered as special cases. Our approach
based on group theory handles the cases of integer and rational magnetic fluxes
in a uniform way and the provided basis could be convenient for further both
analytic and numerical calculations.Comment: 19 pages, 5 figures. accepted to Int. J. Mod. Phys. B (April 2006
Evidence of Skyrmion excitations about in n-Modulation Doped Single Quantum Wells by Inter-band Optical Transmission
We observe a dramatic reduction in the degree of spin-polarization of a
two-dimensional electron gas in a magnetic field when the Fermi energy moves
off the mid-point of the spin-gap of the lowest Landau level, . This
rapid decay of spin alignment to an unpolarized state occurs over small changes
to both higher and lower magnetic field. The degree of electron spin
polarization as a function of is measured through the magneto-absorption
spectra which distinguish the occupancy of the two electron spin states. The
data provide experimental evidence for the presence of Skyrmion excitations
where exchange energy dominates Zeeman energy in the integer quantum Hall
regime at
Bosonization, vicinal surfaces, and hydrodynamic fluctuation theory
Through a Euclidean path integral we establish that the density fluctuations
of a Fermi fluid in one dimension are related to vicinal surfaces and to the
stochastic dynamics of particles interacting through long range forces with
inverse distance decay. In the surface picture one easily obtains the Haldane
relation and identifies the scaling exponents governing the low energy,
Luttinger liquid behavior. For the stochastic particle model we develop a
hydrodynamic fluctuation theory, through which in some cases the large distance
Gaussian fluctuations are proved nonperturbatively
Homology class of a Lagrangian Klein bottle
It is shown that an embedded Lagrangian Klein bottle represents a non-trivial
mod 2 homology class in a compact symplectic four-manifold with
. (In versions 1 and 2, the last assumption was missing.
A counterexample to this general claim and the first proof of the corrected
result have been found by Vsevolod Shevchishin.) As a corollary one obtains
that the Klein bottle does not admit a Lagrangian embedding into the standard
symplectic four-space.Comment: Version 3 - completely rewritten to correct a mistake; Version 4 -
minor edits, added references; AMSLaTeX, 6 page
Modulation theory of quantum tunneling into a Calogero-Sutherland fluid
Quantum hydrodynamics of interacting electrons with a parabolic single
particle spectrum is studied using the Calogero-Sutherland model. The effective
action and modulation equations, describing evolution of periodic excitations
in the fluid, are derived. Applications to the problem of a single electron
tunneling into the FQHE edge state are discussed
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