16,094 research outputs found
Raman Scattering and Anomalous Current Algebra: Observation of Chiral Bound State in Mott Insulators
Recent experiments on inelastic light scattering in a number of insulating
cuprates [1] revealed a new excitation appearing in the case of crossed
polarizations just below the optical absorption threshold. This observation
suggests that there exists a local exciton-like state with an odd parity with
respect to a spatial reflection. We present the theory of high energy large
shift Raman scattering in Mott insulators and interpret the experiment [1] as
an evidence of a chiral bound state of a hole and a doubly occupied site with a
topological magnetic excitation. A formation of these composites is a crucial
feature of various topological mechanisms of superconductivity. We show that
inelastic light scattering provides an instrument for direct measurements of a
local chirality and anomalous terms in the electronic current algebra.Comment: 18 pages, TeX, C Version 3.
Raman Response in Doped Antiferromagnets
The resonant part of the electronic Raman scattering response is
calculated within the model on a planar lattice as a function of
temperature and hole doping, using a finite-temperature diagonalization method
for small systems. Results, directly applicable to experiments on cuprates,
reveal on doping a very pronounced increase of the width of the two-magnon
Raman peak, accompanied by a decrease of the total intensity. At the same time
the peak position does not shift substantially in the underdoped regime.Comment: 11 pages revtex, 3 postscript figures. Minor corrections and changes
from previous version, to be published in Phys. Rev.
Recommended from our members
Fiber optics applications in hostile environments
This Conference focuses on applications of optical fibers in hostile environments. As the introductory paper in this Conference, this communication will trace the evolution of applications of fibers in hostile environments and explore some of the motivations for these applications. A few key examples will be used
Improving the Quality of European Hard Cheese by controlling interactions between Lactic Acid Bacteria and Propionic Acid Bacteria (LAB/PAB) (Stimulation of Propionic Acid Bacteria by Lactic
End of Project ReportTeagasc acknowledges with gratitude grant aid under the EU Framework Programme (FAIR
96-CT-1024).In the manufacture of Swiss-type cheese two successive fermentations
occur. During manufacture, lactic acid bacteria (LAB), particularly
Streptococcus thermophilus, Lactobacillus helveticus and
Lb. delbrueckii subsp. lactis, convert lactose to lactate while,
during ripening, propionic acid bacteria (PAB) convert lactate to
propionic acid, acetic acid and carbon dioxide (CO2). CO2 is
responsible for eye formation and propionic acid results in the typical
nutty flavour of Swiss-type cheese. There have been a few reports of
interactions between a small number of LAB and PAB but the
compounds involved have not been identified. A better
understanding of this phenomenon is necessary to select strains of
PAB for cheesemaking and improve the quality of hard cheeses.
Cheese cannot be used for such a study because of its complexity and
the length of time it is ripened. Hence, a simple whey-based model
developed by Piveteau et al (1995) was successfully used to study the
interactions between LAB and PAB. In this procedure, the LAB were
grown overnight in milk and the whey was collected by centrifugation.
After neutralisation and filter-sterilisation, the growth of strains of PAB
in this whey and in a control whey produced from the same milk by
acidification with lactic acid were compared.
The objectives of this study were to refine the model of Piveteau et al
(1995) to study the interactions between LAB and PAB and to
determine the nature of the stimulant(s) produced by the LAB. * Thirty-two combinations of different commercial strains of PAB and
LAB were evaluated in a modified whey model. None showed any
inhibition and all showed some degree of stimulation but the extent of the stimulation depended on the particular pair of PAB and LAB
used.
* An inhibitor of PAB was found in milk, which prevented the growth
of PAB from low (105 cfu/ml) but not from high inocula (107 cfu/ml).
The inhibitor was heat stable (to autoclaving for 15 min), of low
molecular mass and could be removed by pre-growth of some but not
all starter LAB in milk.
* Growth of P. freudenreichii DPC 3801 in control whey was
stimulated by peptone, tryptone, casein hydrolysed by the crude
proteinase of Lb. helveticus DPC 4571 and by pre-growth of the
lactobacillus in milk, but not by vitamins (riboflavin, thiamine, PABA,
Ca panthothenate, biotin and nicotinic acid) or minerals (MgSO4,
MnCl2, CoCl2 and CuSO4).
* Growth of Lb. helveticus DPC 4571 in milk resulted in significant
increases in peptide and amino acid production but the amino acids
produced did not stimulate the growth of the PAB. Based on these
results it was concluded that the stimulation was due to production of
peptides by the LAB from casein.
* The whey model developed by Piveteau et al (1995) to study the
interactions between PAB and LAB was shown to be reproducible.
Adjustment of the pH of the whey to 5.4 rather than 6.0, incubation
at 24ºC rather than 30ºC and addition of 1% NaCl, to simulate
cheese ripening conditions allowed growth of all the PAB tested.
* Several chromatographic procedures, including ion-exchange, gel
permeation and reverse-phase, high-pressure liquid chromatography
failed to categorically identify the peptide(s) responsible for the
stimulation of the PAB. In some of these chromatographic systems,the stimulatory activity was shown to be present in several peaks
implying that different peptides were involved.European Unio
Fluid/solid transition in a hard-core system
We prove that a system of particles in the plane, interacting only with a
certain hard-core constraint, undergoes a fluid/solid phase transition
The free energy in the Derrida--Retaux recursive model
We are interested in a simple max-type recursive model studied by Derrida and
Retaux (2014) in the context of a physics problem, and find a wide range for
the exponent in the free energy in the nearly supercritical regime
Resonant Two-Magnon Raman Scattering in Cuprate Antiferromagnetic Insulators
We present results of low-temperature two-magnon resonance Raman excitation
profile measurements for single layer Sr_2CuO_2Cl_2 and bilayer YBa_2Cu_3O_{6 +
\delta} antiferromagnets over the excitation region from 1.65 to 3.05 eV. These
data reveal composite structure of the two-magnon line shape and strong
nonmonotic dependence of the scattering intensity on excitation energy. We
analyze these data using the triple resonance theory of Chubukov and Frenkel
(Phys. Rev. Lett., 74, 3057 (1995)) and deduce information about magnetic
interaction and band parameters in these materials.Comment: REVTeX, 4 pages + 2 PostScript (compressed) figure
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