2,151 research outputs found
On an SO(5) unification attempt for the cuprates
In this note we bring out several problems with the SO(5) unification attempt
of Zhang [cond-mat/9610140].Comment: 3 pages, latex (revtex
Spin-charge separation at small lengthscales in the 2D t-J model
We consider projected wavefunctions for the 2D model. For various
wavefunctions, including correlated Fermi-liquid and Luttinger-type
wavefunctions we present the static charge-charge and spin-spin structure
factors. Comparison with recent results from a high-temperature expansion by
Putikka {\it et al.} indicates spin-charge separation at small lengthscales.Comment: REVTEX, 5 pages, 5 figures hardcopies availabl
A numerical and analytical study of two holes doped into the 2D t--J model
Exact diagonalization numerical results are presented for a 32-site square
cluster, with two holes propagating in an antiferromagnetic background
described by the t-J model. We characterize the wave function of the lowest
energy bound state found in this calculation, which has d_{x^2-y^2} symmetry.
Analytical work is presented, based on a Lang-Firsov-type canonical
transformation derived quasiparticle Hamiltonian, that accurately agrees with
numerically determined values for the electron momentum distribution function
and the pair correlation function. We interpret this agreement as strong
support for the validity of this description of the hole quasiparticles.Comment: 3 pages, REVTeX, to appear in the proceedings of the Fifth
International Conference on Spectroscopies in Novel Superconductors,
September 14-18, 1997, Cape Cod, Massachusett
Fermi edge singularities in X-ray spectra of strongly correlated fermions
We discuss the problem of the X-ray absorption in a system of interacting
fermions and, in particular, those features in the X-ray spectra that can be
used to discriminate between conventional Fermi-liquids and novel "strange
metals". Focusing on the case of purely forward scattering off the core-hole
potential, we account for the relevant interactions in the conduction band by
means of the bosonization technique. We find that the X-ray Fermi edge
singularities can still be present, although modified, even if the density of
states vanishes at the Fermi energy, and that, in general, the relationship
between the two appears to be quite subtle.Comment: Latex, 16 pages, Princeton preprin
Superconductivity in CoO Layers and the Resonating Valence Bond Mean Field Theory of the Triangular Lattice t-J model
Motivated by the recent discovery of superconductivity in two dimensional
CoO layers, we present some possibly useful results of the RVB mean field
theory applied to the triangular lattice. Away from half filling, the order
parameter is found to be complex, and yields a fully gapped quasiparticle
spectrum. The sign of the hopping plays a crucial role in the analysis, and we
find that superconductivity is as fragile for one sign as it is robust for the
other. NaCoOHO is argued to belong to the robust case, by
comparing the LDA Fermi surface with an effective tight binding model. The high
frequency Hall constant in this system is potentially interesting, since it is
pointed out to increase linearly with temperature without saturation for T
T.Comment: Published in Physical Review B, total 1 tex + 9 eps files. Erratum
added as separate tex file on November 7, 2003, a numerical factor corrected
in the erratum on Dec 3, 200
Parity (and time-reversal) anomaly in a semiconductor
The physics of a parity anomaly, potentially observable in a narrow-gap
semiconductor, is revisited. Fradkin, Dagotto, and Boyanovsky have suggested
that a Hall current of anomalous parity can be induced by a Peierls distortion
on a domain wall. I argue that a perturbation inducing the parity anomaly must
break the time reversal symmetry, which rules out the Peierls distortion as a
potential cause. I list all possible perturbations that can generate the
anomaly.Comment: 11 pages, 1 figure. Sign errors fixe
Flow equation analysis of the anisotropic Kondo model
We use the new method of infinitesimal unitary transformations to calculate
zero temperature correlation functions in the strong-coupling phase of the
anisotropic Kondo model. We find the dynamics on all energy scales including
the crossover behaviour from weak to strong coupling. The integrable structure
of the Hamiltonian is not used in our approach. Our method should also be
useful in other strong-coupling models since few other analytical methods allow
the evaluation of their correlation functions on all energy scales.Comment: 4 pages RevTeX, 2 eps figures include
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
Particle tunneling through a polarizable insulator
The tunneling probability between two leads connected by a molecule, a chain,
a film, or a bulk polarizable insulator is investigated within a model of an
electron tunneling from lead A to a state higher in energy, describing the
barrier, and from there to lead B. To describe the possibility of energy
exchange with excitations of the molecule or the insulator we couple the
intermediate state to a single oscillator or to a spectrum of these,
respectively. In the single-oscillator case we find for weak coupling that the
tunneling is weakly suppressed by a Debye-Waller-type factor. For stronger
coupling the oscillator gets 'stiff' and we observe a suppression of tunneling
since the effective barrier is increased. The probability for the electron to
excite the oscillator increases with the coupling. In the case of a film, or a
bulk barrier the behavior is qualitatively the same as in the single oscillator
case. An insulating chain, as opposed to a film or a bulk connecting the two
leads,shows an 'orthogonality catastrophe' similar to that of an electronic
transition in a Fermi gas.Comment: 4 pages, 1 figur
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