Effective action approach to strongly correlated fermion systems

We construct a new functional for the single particle Green's function, which is a variant of the standard Baym Kadanoff functional. The stability of the stationary solutions to the new functional is directly related to aspects of the irreducible particle hole interaction through the Bethe Salpeter equation. A startling aspect of this functional is that it allows a simple and rigorous derivation of both the standard and extended dynamical mean field (DMFT) equations as stationary conditions. Though the DMFT equations were formerly obtained only in the limit of infinite lattice coordination, the new functional described in the work, presents a way of directly extending DMFT to finite dimensional systems, both on a lattice and in a continuum. Instabilities of the stationary solution at the bifurcation point of the functional, signal the appearance of a zero mode at the Mott transition which then couples t o physical quantities resulting in divergences at the transition.Comment: 9 page

Mineralization changes substituted type B carbonate of PO43− ion in the bone minerals of an archaeological sample studied using fourier self deconvolution technique

277-282The aim of this study was to describe the compositional changes in the archaeological specimen using FTIR. Fourier deconvolution was applied in the carbonate (500-650 cm−1), phosphate (900-1200 cm−1), and in the amide region (1700-1600 cm−1). The deconvolution of the spectra in the phosphate region 1200-900 cm−1 reveals six components 960 cm−1, 1010 cm−1, 1020 cm−1, 1030 cm−1, 1110 cm−1 and 1120 cm−1. The bone mineral such as CO32−, PO43− particle, collagen, and organic materials were studied in detail from the infrared spectra. The computed parameters such as collagen development, mineralization index, C/P proportion, crystalline index, and maturing of bone help us in characterizing the bone samples. The Low estimation of C/P proportion resulted in changes in Type B carbonate (PO43−) substitution. The absence of phosphate band ~1100 cm−1 and formation of β sheet structure were observed in the samples studied. Increased level of mineralization resulted in the increased in the crystalline nature of the bone samples. The study indicates the utilization of FTIR using self deconvolution technique which helps in understanding the compositional changes in the archaeological sample

Effect of a gap on the decoherence of a qubit

We revisit the problem of the decoherence and relaxation of a central spin coupled to a bath of conduction electrons. We consider both metallic and semiconducting baths to study the effect of a gap in the bath density of states (DOS) on the time evolution of the density matrix of the central spin. We use two weak coupling approximation schemes to study the decoherence. At low temperatures, though the temperature dependence of the decoherence rate in the case of a metallic bath is the same irrespective of the details of the bath, the same is not true for the semiconducting bath. We also calculate the relaxation and decoherence rates as a function of external magnetic fields applied both on the central spin and the bath. We find that in the presence of the gap, there exists a certain regime of fields, for which surprisingly, the metallic bath has lower rates of relaxation and decoherence than the semiconducting bath.Comment: 9 pages, 9 figure

Seroprevalence of hepatitis B virus among patients at a rural tertiary health care centre in South India: a four year study

Background: Infection with the Hepatitis B Virus (HBV) is a global health problem. Epidemiological studies worldwide show wide variations in the prevalence patterns of the Hepatitis B infections. Early detection can contribute substantially to the timely diagnosis of the patients with acute illnesses and to an early treatment and hence, it can limit the transmission of the infection.Aim: To provide a baseline data on the prevalence of Hepatitis B among the patients who were attending Chennai Medical College Hospital and Research Centre, Trichy, Tamilnadu, over a period of 4 years (2010-2013).Methods: This was a retrospective study which was carried out among 19,513 patients who were attending the rural tertiary care teaching hospital, Trichy, over a period of 4 years (January 2010 – December 2013). The sera were screened for the presence of Hepatitis B surface antigen (HBsAg) by HEPACARD. Those found positive on screening test were confirmed by Enzyme linked Immuno-sorbent Assay (ELISA) test.Results: Out of 19,513 sera which were studied, 315 (1.61%) were sero-positive cases. Among the positive cases (315), the seroprevalence in males and females were 73% (230) and 27% (85) respectively and the frequency of HBV among age groups 0-20, 21-40, 41-60, >60 was 5.07% (16), 45.07% (142), 35.9% (113),11425% (36) respectively. Among the positive cases, a majority were in the age group of 21 to 40 years, with a male preponderance (p<0.05). Conclusion: The overall prevalence for this HBsAg marker among the patients who attended the rural tertiary teaching hospital in this study was comparatively similar to that which was reported by other studies from India.

Effects of magnetic field induced chiral-spin interactions on quasi-one-dimensional spin systems

It is known that in certain non-bipartite quasi-one dimensional spin systems in a magnetic field, in addition to the usual Pauli coupling of the spins to the field, new parity breaking three spin interactions, i.e. chiral spin interactions, are induced at higher order due to virtual processes involving the intrinsic electronic nature of the underlying spins. The strenght of these interactions depend strongly on the orientation of the field, a feature which can be exploited to detect chiral effects experimentally. In many spin systems, these chiral interactions are generated and should be taken into account before any comparison with experiments can be made. We study the effect of the chiral interactions on certain quasi-one-dimensional gapped spin half systems and show that they can potentially alter the physics expected from the Pauli coupling alone. In particular, we demonstrate that these terms alter the universality class of the C-IC transition in spin-tubes. More interestingly, in weakly coupled XX zig-zag ladders, we find that the field induced chiral term can close the singlet gap and drive a second order transition in the non-magnetic singlet sector, which manifests itself as a two component Luttinger liquid-like behaviour in the spin correlation functions. Finally, we discuss the relevance of our results to experiments.Comment: RevTex, 11 pages, 3 figure

Dynamical Mean Field Theory of the Antiferromagnetic Metal to Antiferromagnetic Insulator Transition

We study the antiferromagnetic metal to antiferromagnetic insulator using dynamical mean field theory and exact diagonalization methods. We find two qualitatively different behaviors depending on the degree of magnetic correlations. For strong correlations combined with magnetic frustration, the transition can be described in terms of a renormalized slater theory, with a continuous gap closure driven by the magnetism but strongly renormalized by correlations. For weak magnetic correlations, the transition is weakly first order.Comment: 4 pages, uses epsfig,4 figures,notational errors rectifie

Coulombian Disorder in Periodic Systems

We study the effect of unscreened charged impurities on periodic systems. We show that the long wavelength component of the disorder becomes long ranged and dominates static correlation functions. On the other hand, because of the statistical tilt symmetry, dynamical properties such as pinning remain unaffected. As a concrete example, we focus on the effect of Coulombian disorder generated by charged impurities, on 3D charge density waves with non local elasticity. We calculate the x-ray intensity and find that it is identical to the one produced by thermal fluctuations in a disorder-free smectic-A. We discuss the consequences of these results for experiments.Comment: 11 pages, 3 figures, revtex

Non-Abelian bosonization of the frustrated antiferromagnetic spin-1/2 chain

We study the spin-1/2 chain with nearest neighbor ($\kappa_1$) and next-nearest neighbor ($\kappa_2$) interactions in the regime $\kappa_2\gg \kappa_1$, which is equivalent to two chains with a `zig-zag' interaction. In the continuum limit, this system is described in term of two coupled level-1 WZW field theories. We illustrate its equivalence with four off-critical Ising models (Majorana fermions). This description is used to investigate the opening of a gap as a function of $\kappa_1$ and the associated spontaneous breakdown of parity. We calculate the dynamic spin structure factor near the wavevectors accessible to the continuum limit. We comment on the nonzero string order parameter and show the presence of a hidden ${\Bbb Z}_2\times{\Bbb Z}_2$ symmetry via a nonlocal transformation on the microscopic Hamiltonian. For a ferromagnetic interchain coupling, the model is conjectured to be critical, with different velocities for the spin singlet and spin triplet excitations.Comment: 20 pages, RevTeX, 1 postscript figure. Minor corrections added, resulting in different velocity renormalizations; no qualitative change in conclusion

Lattice Instability in the Spin-Ladder System under Magnetic Field

We study theoretically the lattice instability in the spin gap systems under magnetic field. With the magnetic field larger than a critical value h_{c1}, the spin gap is collapsed and the magnetization arises. We found that the lattice distortion occurs in the spin-ladder at an incommensurate wavevector corresponding to the magnetization, while it does not occur in the Haldane system. At low temperatures the magnetization curve shows a first order phase transition with this lattice distortion.Comment: 10 pages, REVTEX, 2 figures(ps file), minor change

Dynamical Structure Factors of the S=1/2 Bond-Alternating Spin Chain with a Next-Nearest-Neighbor Interaction in Magnetic Fields

The dynamical structure factor of the S=1/2 bond-alternating spin chain with a next-nearest-neighbor interaction in magnetic field is investigated using the continued fraction method based on the Lanczos algorithm. When the plateau exists on the magnetization curve, the longitudinal dynamical structure factor shows a large intensity with a periodic dispersion relation, while the transverse one shows a large intensity with an almost dispersionless mode. The periodicity and the amplitude of the dispersion relation in the longitudinal dynamical structure factor are sensitive to the coupling constants. The dynamical structure factor of the S=1/2 two-leg ladder in magnetic field is also calculated in the strong interchain-coupling regime. The dynamical structure factor shows gapless or gapful behavior depending on the wave vector along the rung.Comment: 8 pages, 4 figures, to appear in Journal of the Physical Society of Japan, vol. 69, no. 10, (2000