389 research outputs found
Fr\"ohlich Polarons from 0D to 3D: Concepts and Recent Developments
I analyse our present understanding of the Froehlich polaron with emphasis on
the response properties, in particular optical absorption.Comment: 28 pages, 17 figures, invited lecture at the ESF Exploratory Workshop
EW05-105 "Mott's Physics in Nanowires and Quantum Dots", University of
Cambridge, United Kingdom, 31 July - 2 August 200
Note on the Path-Integral Variational Approach in the Many-Body Theory
I discuss how a variatonal approach can be extended to systems of identical
particles (in particular fermions) within the path-integral treatment. The
applicability of the many-body variational principle for path integrals is
illustrated for different model systems, and is shown to crucially depend on
whether or not a model system possesses the proper symmetry with respect to
permutations of identical particles.Comment: 15 pages, 1 figure, E-mail address: [email protected]
Sum Rule for the Optical Absorption of an Interacting Many-Polaron Gas
A sum rule for the first frequency moment of the optical absorption of a
many-polaron system is derived, taking into account many-body effects in the
system of constituent charge carriers of the many-polaron system. In our
expression for the sum rule, the electron-phonon coupling and the many-body
effects in the electron (or hole) system formally decouple, so that the
many-body effects can be treated to the desired level of approximation by the
choice of the dynamical structure factor of the electron (hole) gas. We
calculate correction factors to take into account both low and high
experimental cutoff frequencies.Comment: 16 pages, 3 figures, revised version; new results adde
Ground state and optical conductivity of interacting polarons in a quantum dot
The ground-state energy, the addition energies and the optical absorption
spectra are derived for interacting polarons in parabolic quantum dots in three
and two dimensions. A path integral formalism for identical particles is used
in order to take into account the fermion statistics. The approach is applied
to both closed-shell and open-shell systems of interacting polarons. Using a
generalization of the Jensen-Feynman variational principle, the ground-state
energy of a confined N-polaron system is analyzed as a function of N and of the
electron-phonon coupling constant. As distinct from the few-electron systems
without the electron-phonon interaction, three types of spin polarization are
possible for the ground state of the few-polaron systems: (i) a spin-polarized
state, (ii) a state where the spin is determined by Hund's rule, (iii) a state
with the minimal possible spin. A transition from a state fulfilling Hund's
rule, to a spin-polarized state occurs when decreasing the electron density. In
the strong-coupling limit, the system of interacting polarons turns into a
state with the minimal possible spin. These transitions should be
experimentally observable in the optical absorption spectra of quantum dots.Comment: 33 pages, 9 figures, E-mail addresses: [email protected],
[email protected], [email protected], [email protected],
accepted for Phys. Rev.
Path integral formulation of the tunneling dynamics of a superfluid Fermi gas in an optical potential
To describe the tunneling dynamics of a stack of two-dimensional fermionic
superfluids in an optical potential, we derive an effective action functional
from a path integral treatment. This effective action leads, in the saddle
point approximation, to equations of motion for the density and the phase of
the superfluid Fermi gas in each layer. In the strong coupling limit (where
bosonic molecules are formed) these equations reduce to a discrete nonlinear
Schrodinger equation, where the molecular tunneling amplitude is reduced for
large binding energies. In the weak coupling (BCS) regime, we study the
evolution of the stacked superfluids and derive an approximate analytical
expression for the Josephson oscillation frequency in an external harmonic
potential. Both in the weak and intermediate coupling regimes the detection of
the Josephson oscillations described by our path integral treatment constitutes
experimental evidence for the fermionic superfluid regime.Comment: 13 pages + 2 figure
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