526 research outputs found
Luttinger theorem for a spin-density-wave state
We obtained the analog of the Luttinger relation for a commensurate
spin-density-wave state. We show that while the relation between the area of
the occupied states and the density of particles gets modified in a simple and
predictable way when the system becomes ordered, a perturbative consideration
of the Luttinger theorem does not work due to the presence of an anomaly
similar to the chiral anomaly in quantum electrodynamics.Comment: 4 pages, RevTeX, 1 figure embedded in the text, ps-file is also
available at http://lifshitz.physics.wisc.edu/www/morr/morr_homepage.htm
Bond-impurity induced bound states in disordered spin-1/2 ladders
We discuss the effect of weak bond-disorder in two-leg spin ladders on the
dispersion relation of the elementary triplet excitations with a particular
focus on the appearance of bound states in the spin gap. Both the cases of
modified exchange couplings on the rungs and the legs of the ladder are
analyzed. Based on a projection on the single-triplet subspace, the
single-impurity and small cluster problems are treated analytically in the
strong-coupling limit. Numerically, we study the problem of a single impurity
in a spin ladder by exact diagonalization to obtain the low-lying excitations.
At finite concentrations and to leading order in the inter-rung coupling, we
compare the spectra obtained from numerical diagonalization of large systems
within the single-triplet subspace with the results of diagrammatic techniques,
namely low-concentration and coherent-potential approximations. The
contribution of small impurity clusters to the density of states is also
discussed.Comment: 9 pages REVTeX4 including 7 figures, final version; Fig. 5 modifie
Pairing dynamics in strongly correlated superconductivity
Confirmation of the phononic origin of Cooper pair formation in
superconductors came with the demonstration that the interaction was retarded
and that the corresponding energy scales were associated with phonons. Using
cellular dynamical mean-field theory for the two-dimensional Hubbard model, we
identify such retardation effects in d-wave pairing and associate the
corresponding energy scales with short-range spin fluctuations. We find which
frequencies are relevant for pairing as a function of interaction strength and
doping and show that the disappearance of superconductivity on the overdoped
side coincides with the disappearance of the low energy feature in the
antiferromagnetic fluctuations, as observed in neutron scattering experiments.Comment: LaTeX, 8 pages, 8 figure
Jacobson generators, Fock representations and statistics of sl(n+1)
The properties of A-statistics, related to the class of simple Lie algebras
sl(n+1) (Palev, T.D.: Preprint JINR E17-10550 (1977); hep-th/9705032), are
further investigated. The description of each sl(n+1) is carried out via
generators and their relations, first introduced by Jacobson. The related Fock
spaces W_p (p=1,2,...) are finite-dimensional irreducible sl(n+1)-modules. The
Pauli principle of the underlying statistics is formulated. In addition the
paper contains the following new results: (a) The A-statistics are interpreted
as exclusion statistics; (b) Within each W_p operators B(p)_1^\pm, ...,
B(p)_n^\pm, proportional to the Jacobson generators, are introduced. It is
proved that in an appropriate topology the limit of B(p)_i^\pm for p going to
infinity is equal to B_i^\pm, where B_i^\pm are Bose creation and annihilation
operators; (c) It is shown that the local statistics of the degenerated
hard-core Bose models and of the related Heisenberg spin models is p=1
A-statistics.Comment: LaTeX-file, 33 page
The effect of Fermi surface curvature on low-energy properties of fermions with singular interactions
We discuss the effect of Fermi surface curvature on long-distance/time
asymptotic behaviors of two-dimensional fermions interacting via a gapless mode
described by an effective gauge field-like propagator. By comparing the
predictions based on the idea of multi-dimensional bosonization with those of
the strong- coupling Eliashberg approach, we demonstrate that an agreement
between the two requires a further extension of the former technique.Comment: Latex, 4+ pages. Phys. Rev. Lett., to appea
Coexistence of superconductivity and a spin density wave in pnictides: Gap symmetry and nodal lines
We investigate the effect of a spin-density wave (SDW) on
superconductivity in Fe-based superconductors. We show that, contrary to the
common wisdom, no nodes open at the new, reconnected Fermi surfaces when the
hole and electron pockets fold down in the SDW state, despite the fact that the
gap changes sign between the two pockets. Instead, the order
parameter preserves its sign along the newly formed Fermi surfaces. The
familiar experimental signatures of an symmetry are still preserved,
although they appear in a mathematically different way. For a regular case
( the nodes do appear in the SDW state. This distinction suggests a
novel simple way to experimentally separate an state from a regular
in the pnictides. We argue that recently published thermal conductivity
data in the coexisting state are consistent with the but not the
state
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