220 research outputs found
Gauge-invariant dressed fermion propagator in massless QED_3
The infrared behaviour of the gauge-invariant dressed fermion propagator in
massless QED_3 is discussed for three choices of dressing. It is found that
only the propagator with the isotropic (in three Euclidean dimensions) choice
of dressing is acceptable as the physical fermion propagator. It is explained
that the negative anomalous dimension of this physical fermion does not
contradict any field-theoretical requirement.Comment: 10 pages; references added; minor changes in tex
Theory of Asymmetric Tunneling in the cuprate superconductors
We explain quantitatively, within the Gutzwiller-Resonating Valence Bond
theory, the puzzling observation of tunneling conductivity between a metallic
point and a cuprate high- superconductor which is markedly asymmetric
between positive and negative voltage biases. The asymmetric part does not have
a "coherence peak" but does show structure due to the gap. The fit to data is
satisfactory within the over-simplifications of the theory; in particular, it
explains the marked "peak-dip-hump" structure observed on the hole side and a
number of other qualitative observations. This asymmetry is strong evidence for
the projective nature of the ground state and hence for "t-J" physics.Comment: 5 pages, 3 figures, revised 6/1/0
Fermion propagator for QED_3 in the IR domain
We evaluate the fermion propagator in parity-conserving QED_3 with N
flavours, in the context of an IR domain approximation. This provides results
which are non-perturbative in the loopwise expansion sense. We include
fermion-loop effects, and show that they are relevant to the chiral symmetry
breaking phenomenon, that can be understood in this context.Comment: 11 pages, LaTeX; typo corrected in Eq.3
Thermodynamics of the BCS-BEC crossover
We present a self-consistent theory for the thermodynamics of the BCS-BEC
crossover in the normal and superfluid phase which is both conserving and
gapless. It is based on the variational many-body formalism developed by
Luttinger and Ward and by DeDominicis and Martin. Truncating the exact
functional for the entropy to that obtained within a ladder approximation, the
resulting self-consistent integral equations for the normal and anomalous Green
functions are solved numerically for arbitrary coupling. The critical
temperature, the equation of state and the entropy are determined as a function
of the dimensionless parameter , which controls the crossover from the
BCS-regime of extended pairs to the BEC-regime of tightly bound molecules. The
tightly bound pairs turn out to be described by a Popov-type approximation for
a dilute, repulsive Bose gas. Even though our approximation does not capture
the critical behaviour near the continuous superfluid transition, our results
provide a consistent picture for the complete crossover thermodynamics which
compare well with recent numerical and field-theoretic approaches at the
unitarity point.Comment: published versio
Elusive physical electron propagator in QED-like effective theories
We study the previously conjectured form of the physical electron propagator
and its allegedly Luttinger type of behavior in the theory of the pseudogap
phase of high-temperature copper-oxide superconductors and other effective
QED-like models. We demonstrate that, among a whole family of seemingly
gauge-invariant functions, the conjectured "stringy ansatz" for the electron
propagator is the only one that is truly invariant. However, contrary to the
results of the earlier works, it appears to have a negative anomalous
dimension, which makes it a rather poor candidate to the role of the physical
electron propagator. Instead, we argue that the latter may, in fact, feature a
"super-Luttinger" behavior characterized by a faster than any power-law decay:
G(x) ~ exp(-const ln^2|x|).Comment: Latex, 10 pages, no figure
Effect of gauge boson mass on the phase structure of QED
Dynamical chiral symmetry breaking (DCSB) in QED with finite gauge
boson mass is
studied in the framework of the rainbow approximation of Dyson-Schwinger
equations.
By adopting a simple gauge boson propagator ansatz at finite temperature, we
first numerically solve the
Dyson-Schwinger equation for the fermion self-energy to
determine the chiral phase diagram of QED with finite gauge boson mass
at finite chemical potential and finite temperature, then we study the
effect of the finite gauge mass on the phase diagram of QED. It is found
that the gauge boson mass suppresses the occurrence of
DCSB. The area of the region in the chiral phase diagram corresponding to
DCSB phase decreases as
the gauge boson mass increases. In
particular, chiral symmetry gets restored when is above a
certain critical value. In this paper, we use DCSB to describe the
antiferromagnetic order and use the gauge boson mass to describe the
superconducting order. Our results give qualitatively a physical
picture on the competition and coexistence between antiferromagnetic
order and superconducting orders in high temperature cuprate superconductors.Comment: 10 pages, 2 figure
Anomalous Dimension of Dirac's Gauge-Invariant Nonlocal Order Parameter in Ginzburg-Landau Field Theory
In a Ginzburg-Landau theory with fields, the anomalous dimension of the
gauge-invariant nonlocal order parameter defined by the long-distance limit of
Dirac's gauge-invariant two-point function is calculated. The result is exact
for all to first order in , and for all
to first order in , and coincides with the previously calculated
gauge-dependent exponent in the Landau gauge.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of
paper http://www.physik.fu-berlin.de/~kleinert/35
Low-energy Spectra of the t-J-Type Models Studied by Variational Approach
We discuss recent progress of understanding the phenomena observed in high Tc
cuprates by studying the d-wave resonating-valence-bond (d-RVB) based trial
wave functions for the 2-dimensional t-J-type models. Treat exactly the strong
correlation between electrons by numerical approach, we examine the evolution
of ground states described by different variational wave functions and
properties of the quasi-hole and -particle excitations of the d-RVB
superconducting (SC) state. Properties related to the Fermi surface geometry
deduced from quasi-hole energy dispersion of the SC state is shown to be
consistent with the observation by photoemission spectroscopy. With the
calculated spectral weights (SW's) for adding and removing an electron, we
found not only the anti-correlation between conductance peak height and width
between peaks seen in tunneling experiments, but also unique properties due to
strong correlation which need to be verified by future experiments.Comment: 6 revtex pages with 5 (.eps) figures. To appear in a special volume
of Journal of Magnetism and Magnetic Materials for the ICM 2006 proceeding
Comment on electron spectral function and algebraic spin liquid for the normal state of underdoped high Tc superconductors (multiple letters
In a recent Letter [1], Rantner and Wen made a theoretical prediction of the power-law behavior of the electron spectral function in the pseudogap phase of underdoped cuprates, reminiscent of that in the one-dimensional Luttinger liquid
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