1,417 research outputs found
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
Electron concentration effects on the Shastry-Sutherland phase stability in Ce_{2-x}Pd_{2+y}In_{1-z} solid solutions
The stability of a Shastry-Sutherland ShSu phase as a function of electron
concentration is investigated through the field dependence of thermal and
magnetic properties of the solid solution Ce_{2-x}Pd_{2+y}In_{1-z} in the
antiferromagnetic branch. In these alloys the electronic (holes) variation is
realized by increasing concentration. The AF transition T_M decreases from
3.5K to 2.8K as concentration increases from y=0.2 to y=0.4. By applying
magnetic field, the ShSu phase is suppressed once the field induced
ferromagnetic polarization takes over at a critical field B_{cr} which
increases with content. A detailed analysis around the critical point
reveals a structure in the maximum of the dM/dB derivative, which is related
with incipient steps in the magnetization M(B) as predicted by the theory for
the ShSu lattice. The crossing of M(B) isotherms, observed in ShSu prototype
compounds, is also analyzed. The effect of substitution by is
interpreted as an increase of the number of 'holes' in the conduction band and
results in a unique parameter able to describe the variation of the magnetic
properties along the studied range of concentration.Comment: 8 pages, 11 figure
Microscopic mechanism for the 1/8 magnetization plateau in SrCu_2(BO_3)_2
The frustrated quantum magnet SrCu_2(BO_3)_2 shows a remarkably rich phase
diagram in an external magnetic field including a sequence of magnetization
plateaux. The by far experimentally most studied and most prominent
magnetization plateau is the 1/8 plateau. Theoretically, one expects that this
material is well described by the Shastry-Sutherland model. But recent
microscopic calculations indicate that the 1/8 plateau is energetically not
favored. Here we report on a very simple microscopic mechanism which naturally
leads to a 1/8 plateau for realistic values of the magnetic exchange constants.
We show that the 1/8 plateau with a diamond unit cell benefits most compared to
other plateau structures from quantum fluctuations which to a large part are
induced by Dzyaloshinskii-Moriya interactions. Physically, such couplings
result in kinetic terms in an effective hardcore boson description leading to a
renormalization of the energy of the different plateaux structures which we
treat in this work on the mean-field level. The stability of the resulting
plateaux are discussed. Furthermore, our results indicate a series of stripe
structures above 1/8 and a stable magnetization plateau at 1/6. Most
qualitative aspects of our microscopic theory agree well with a recently
formulated phenomenological theory for the experimental data of SrCu_2(BO_3)_2.
Interestingly, our calculations point to a rather large ratio of the magnetic
couplings in the Shastry-Sutherland model such that non-perturbative effects
become essential for the understanding of the frustrated quantum magnet
SrCu_2(BO_3)_2.Comment: 24 pages, 24 figure
Solution of Some Integrable One-Dimensional Quantum Systems
In this paper, we investigate a family of one-dimensional multi-component
quantum many-body systems. The interaction is an exchange interaction based on
the familiar family of integrable systems which includes the inverse square
potential. We show these systems to be integrable, and exploit this
integrability to completely determine the spectrum including degeneracy, and
thus the thermodynamics. The periodic inverse square case is worked out
explicitly. Next, we show that in the limit of strong interaction the "spin"
degrees of freedom decouple. Taking this limit for our example, we obtain a
complete solution to a lattice system introduced recently by Shastry, and
Haldane; our solution reproduces the numerical results. Finally, we emphasize
the simple explanation for the high multiplicities found in this model
Exact solution and spectral flow for twisted Haldane-Shastry model
The exact solution of the spin chain model with exchange is found for
twisted boundary conditions. The spectrum thus obtained can be reproduced by
the asymptotic Bethe ansatz. The spectral flow of each eigenstate is determined
exactly as a function of the twist angle. We find that the period for
the ground state nicely fits in with the notion of fractional exclusion
statistics.Comment: 4 pages, revtex, 1 figure available on request, to appear in PR
A Class of Parameter Dependent Commuting Matrices
We present a novel class of real symmetric matrices in arbitrary dimension
, linearly dependent on a parameter . The matrix elements satisfy a set
of nontrivial constraints that arise from asking for commutation of pairs of
such matrices for all , and an intuitive sufficiency condition for the
solvability of certain linear equations that arise therefrom. This class of
matrices generically violate the Wigner von Neumann non crossing rule, and is
argued to be intimately connected with finite dimensional Hamiltonians of
quantum integrable systems.Comment: Latex, Added References, Typos correcte
Evaluation of pharmacovigilance concepts among healthcare professionals in Davangere, Karnataka, India
Background: Adverse drug reactions are one of the leading causes of morbidity and mortality worldwide. Timely detection and reporting of adverse drug events through pharmacovigilance is the best tool we have to prevent adverse drug reaction. One of the major reasons for underutilization of pharmacovigilance in India is deficit in awareness, attitude and practice of pharmacovigilance. The objective of this study was to assess these parameters among healthcare professionals in our hospital.Methods: 200 health care professionals (post graduate students, undergraduate students, interns and nurses) took part in the study. A pre-designed questionnaire structured to obtain information on pharmacovigilance was used for evaluation. Questionnaire also enquired on factors that deter respondents from reporting.Results: Among undergraduates, the satisfactory responses for knowledge, awareness and practice of pharmacovigilance were 12%, 72% and 42% respectively and for postgraduates it was 52%, 48% and 26% respectively. For interns it was 4%, 38% and 8 % respectively and nurses 8%, 18% and 26% respectively. Only 1% of undergraduates and 14% of postgraduates showed satisfactory responses to all three categories evaluated. Undergraduate students had a significantly higher awareness scores among the categories (p<0.05). When it comes to knowledge and practice there was not much differences between groups. Lack of time to report was the most cited factor across all categories discouraging reporting.Conclusions: Results are encouraging among undergraduate students, but not significantly better than postgraduates. The poor performance among interns and nurses is due to lack of awareness. A strong basic foundation course regarding pharmacovigilance in academics will help in effective implementation of pharmacovigilance
Lax pair for SU(n) Hubbard model
For one dimensional SU(n) Hubbard model, a pair of Lax operators are derived,
which give a set of fundamental equations for the quantum inverse scattering
method under both periodic and open boundary conditions. This provides another
proof of the integrability of the model under periodic boundary condition.Comment: Latex file, 7 pages, little change adde
A 2D quantum antiferromagnet with a four-fold degenerate valence-bond-solid ground state
We study the competition between antiferromagnetic order and valence bond
solid formation in a two-dimensional frustrated spin-1/2 model. The J1-J2 model
on the square lattice is further frustrated by introducing products of
three-spin projectors which stabilize four dimer-product states as degenerate
ground states. These four states are reminiscent of the dimerized singlet
ground state of the Shastry-Sutherland model. Using exact diagonalizations, we
study the evolution of the ground state by varying theratio of interactions.
For a large range of parameters (J2 > 0.25J1), our model shows a direct
transition between the valence-bond-solid phase and the collinear
antiferromagnetic phase. For small values of J2, several intermediate phases
appear which are also analyzed
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