15,517 research outputs found
Spin susceptibility of underdoped cuprates: the case of Ortho-II YBa_2Cu_3O_{6.5}
Recent inelastic neutron scattering measurements found that the spin
susceptibility of detwinned and highly ordered ortho-II YBa_2Cu_3O_{6.5}
exhibits, in both the normal and superconducting states, one-dimensional
incommensurate modulations at low energies which were interpreted as a
signature of dynamic stripes. We propose an alternative model based on
quasiparticle transitions between the arcs of a truncated Fermi surface. Such
transitions are resonantly enhanced by scattering to the triplet spin
resonance. We show that the anisotropy in the experimental spin response is
consistent with this model if the gap at the saddle points is anisotropic.Comment: 5 fives, 3 postscript figure
APPLICATION OF THE MODULARIZATION CONCEPT TO SATELLITE TAPE RECORDERS
Application of the modularization concept to satellite tape recorder
Magnetic domain formation in itinerant metamagnets
We examine the effects of long-range dipolar forces on metamagnetic
transitions and generalize the theory of Condon domains to the case of an
itinerant electron system undergoing a first-order metamagnetic transition. We
demonstrate that within a finite range of the applied field, dipolar
interactions induce a spatial modulation of the magnetization in the form of
stripes or bubbles. Our findings are consistent with recent observations in the
bilayer ruthenate SrRuO.Comment: 4 pages, 3 figures, minor changes, references adde
Spin Gaps in Coupled t-J Ladders
Spin gaps in coupled - ladders are investigated by exact
diagonalization of small clusters up to 48 sites. At half-filling, the
numerical results for the triplet excitation spectrum are in very good
agreement with a second order perturbation expansion in term of small
inter-ladder and intra-ladder exchange couplings between rungs
(). The band of local triplet excitations moving
coherently along the ladder (with momenta close to ) is split by the
inter-ladder coupling. For intermediate couplings finite size scaling is used
to estimate the spin gap. In the isotropic infinite 4-chain system (two coupled
ladders) we find a spin gap of , roughly half of the single ladder
spin gap. When the system is hole doped, bonding and anti-bonding bound pairs
of holes can propagate coherently along the chains and the spin gap remains
finite.Comment: 11 pages, 5 figures, uuencoded form of postscript files of figures
and text, LPQTH-94/
Strong Coupling Expansions for Antiferromagnetic Heisenberg S=1/2 Ladders
The properties of antiferromagnetic Heisenberg ladders with
2, 3, and 4 chains are expanded in the ratio of the intra- and interchain
coupling constants. A simple mapping procedure is introduced to relate the 4
and 2-chain ladders which holds down to moderate values of the expansion
parameters. A second order calculation of the spin gap to the lowest triplet
excitation in the 2- and 4-chain ladders is found to be quite accurate even at
the isotropic point where the couplings are equal. Similar expansions and
mapping procedures are presented for the 3-chain ladders which are in the same
universality class as single chains.Comment: 10 physical pages, uuencoded compressed PostScript file including 12
figures, ETH-TH/942
Entangled and disentangled evolution for a single atom in a driven cavity
For an atom in an externally driven cavity, we show that special initial
states lead to near-disentangled atom-field evolution, and superpositions of
these can lead to near maximally-entangled states. Somewhat counterintutively,
we find that (moderate) spontaneous emission in this system actually leads to a
transient increase in entanglement beyond the steady-state value. We also show
that a particular field correlation function could be used, in an experimental
setting, to track the time evolution of this entanglement
Spin and charge gaps in the one-dimensional Kondo-lattice model with Coulomb interaction between conduction electrons
The density-matrix renormalization-group method is applied to the
one-dimensional Kondo-lattice model with the Coulomb interaction between the
conduction electrons. The spin and charge gaps are calculated as a function of
the exchange constant and the Coulomb interaction . It is shown that
both the spin and charge gaps increase with increasing and . The spin
gap vanishes in the limit of for any with an
exponential form, . The
exponent, , is determined as a function of . The charge gap
is generally much larger than the spin gap. In the limit of ,
the charge gap vanishes as for but for a finite
it tends to a finite value, which is the charge gap of the Hubbard model.Comment: RevTeX, 4 pages, 3 Postscript figure
Magnon Dispersion in the Field-Induced Magnetically Ordered Phase of TlCuCl3
The magnetic properties of the interacting dimer system TlCuCl3 are
investigated within a bond-operator formulation. The observed field-induced
staggered magnetic order perpendicular to the field is described as a Bose
condensation of magnons which are linear combinations of dimer singlet and
triplet modes. This technique accounts for the magnetization curve and for the
field dependence of the magnon dispersion curves observed by high-field neutron
scattering measurements.Comment: 4 pages, 4 figures, REVTeX
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