2,259 research outputs found
Pressure-induced phase transition and bi-polaronic sliding in a hole-doped Cu_2O_3 ladder system
We study a hole-doped two-leg ladder system including metal ions, oxygen, and
electron-lattice interaction, as a model for Sr_{14-x}Ca_xCu_{24}O_{41-\delta}.
Single- and bi-polaronic states at 1/4-hole doping are modeled as functions of
pressure by applying an unrestricted Hartree-Fock approximation to a multiband
Peierls-Hubbard Hamiltonian. We find evidence for a pressure-induced phase
transition between single-polaron and bi-polaron states. The electronic and
phononic excitations in those states, including distinctive local lattice
vibrational modes, are calculated by means of a direct-space Random Phase
approximation. Finally, as a function of pressure, we identify a transition
between site- and bond-centered bi-polarons, accompanied by a soft mode and a
low-energy charge-sliding mode. We suggest comparisons with available
experimented data
Resonant Raman Scattering in Antiferromagnets
Two-magnon Raman scattering provides important information about electronic
correlations in the insulating parent compounds of high- materials. Recent
experiments have shown a strong dependence of the Raman signal in
geometry on the frequency of the incoming photon. We present an analytical and
numerical study of the Raman intensity in the resonant regime. It has been
previously argued by one of us (A.Ch) and D. Frenkel that the most relevant
contribution to the Raman vertex at resonance is given by the triple resonance
diagram. We derive an expression for the Raman intensity in which we
simultaneously include the enhancement due to the triple resonance and a final
state interaction. We compute the two-magnon peak height (TMPH) as a function
of incident frequency and find two maxima at and . We argue that the
high-frequency maximum is cut only by a quasiparticle damping, while the
low-frequency maximum has a finite amplitude even in the absence of damping. We
also obtain an evolution of the Raman profile from an asymmetric form around
to a symmetric form around . We
further show that the TMPH depends on the fermionic quasiparticle damping, the
next-nearest neighbor hopping term and the corrections to the
interaction vertex between light and the fermionic current. We discuss our
results in the context of recent experiments by Blumberg et al. on
and and R\"{u}bhausen et al. on
and show that the triple resonance theory yields a qualitative
and to some extent also quantitative understanding of the experimental data.Comment: 19 pages, RevTeX, 16 figures embedded in the text, ps-file is also
available at http://lifshitz.physics.wisc.edu/www/morr/morr_homepage.htm
Weak ferromagnetic spin and charge stripe order in La[sub 5/3]Sr[sub 1/3]NiO[sub 4]
We present magnetization and specific heat data of a La5/3Sr1/3NiO4 single
crystal in high magnetic fields. From the charge and spin stripe ordering
temperatures, as well as a magnetic low temperature transition, we have
constructed the electronic phase diagram for fields up to 14 Tesla. While the
charge stripe ordering temperature TCO is independent of the magnetic field,
there is a significant shift of the spin stripe ordering temperature TSO of
about 1.5 K/ Tesla, if the magnetic fields are applied parallel to the
NiO2-planes. The specific heat measurements indicate a large anomalous entropy
change at TCO. In contrast, no significant entropy change is observed at the
spin stripe transition. The high field magnetization experiments reveal the
presence of in-plane weak ferromagnetic moments in the charge stripe ordered
phase. From a phenomenological analysis, the magnetic correlation length of
these moments is determined. We suggest that the weak ferromagnetism is due
either to the presence of bond-centered charge stripes or to double exchange
interactions across site-centered charge stripes.Comment: In v2, spelling of author names has been change
Long‐term management of the successful adult liver transplant: 2012 practice guideline by the American Association for the Study of Liver Diseases and the American Society of Transplantation
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95693/1/23566_ftp.pd
Influence of oxygen ordering kinetics on Raman and optical response in YBa_2Cu_3O_{6.4}
Kinetics of the optical and Raman response in YBa_2Cu_3O_{6.4} were studied
during room temperature annealing following heat treatment. The superconducting
T_c, dc resistivity, and low-energy optical conductivity recover slowly,
implying a long relaxation time for the carrier density. Short relaxation times
are observed for the B_{1g} Raman scattering -- magnetic, continuum, and phonon
-- and the charge transfer band. Monte Carlo simulations suggest that these two
relaxation rates are related to two length scales corresponding to local oxygen
ordering (fast) and long chain and twin formation (slow).Comment: REVTeX, 3 pages + 4 PostScript (compressed) figure
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