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Navadwīp, India

Pugatch R.,Institute for Advanced Study | Bhattacharyya D.,Santipur College | Amir A.,Harvard University | Sagi Y.,U.S. National Institute of Standards and Technology | Davidson N.,Weizmann Institute of Science
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

The electromagnetically induced transparency (EIT) spectrum of atoms diffusing in and out of a narrow beam is measured and shown to manifest the two-dimensional δ-function anomaly in a classical setting. In the limit of small-area beams, the EIT line shape is independent of power, and equal to the renormalized local density of states of a free particle Hamiltonian. The measured spectra for different powers and beam sizes collapses to a single universal curve with a characteristic logarithmic Van Hove singularity close to resonance. © 2014 American Physical Society. Source

Bhattacharyya D.,Santipur College | Ghosh A.,Visva Bharati | Bandyopadhyay A.,Visva Bharati | Saha S.,Saha Institute of Nuclear Physics | De S.,Saha Institute of Nuclear Physics
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2015

We report the observation of electromagnetically induced transparency (EIT) in a six-level Λ-type system in atomic Rb vapor containing both 87Rb and 85Rb. The experimental observation includes five velocity selective optically pumped (VSOP) absorption dips for both 87Rb and 85Rb. The EIT signal appears on the background of one such VSOP absorption dips. The measured EIT linewidth () shows sub-natural ( ) values for both lower and higher values of pump Rabi-frequencies. The density matrix based theoretical model for the six-level system is developed and solved numerically by taking into account the Doppler broadening. A complete analytical solution (non perturbative) for a three level Λ-type system has been obtained and compared with the experimentally observed sub-natural EIT linewidth. The simulated spectra are in good agreement with the experimental findings. © 2015 IOP Publishing Ltd. Source

Biswas S.,Kalyani University | Kar T.,Utah State University | Sarkar S.,Kalyani University | Sarkar S.,Santipur College | Dey K.,Kalyani University
Journal of Coordination Chemistry | Year: 2012

Some Mn(III) complexes of N,N-(2-hydroxy)propylenebis(acetylacetoneimine) (abbreviated to H 2L 1) and N,N-(2-hydroxy)propylenebis(2- imino-3-oximino)butane (abbreviated to H 2L 2), [Mn(III)(Lig)(X)] (where Lig stands for the dianion of the Schiff-base ligands and X stands for CH 3COO -, Cl -, Br -, I -) were synthesized. The complexes are characterized with the help of elemental analyses, magnetic moments, spectroscopic data (UV-Vis, infrared), and molecular weight determination (measured by Rast's method). The structures of the complexes were obtained using density functional theory (DFT). DFT calculation shows that 1-4 and 8 are trigonal-bipyramidal whereas 5-7 are square-pyramidal. © 2012 Copyright Taylor and Francis Group, LLC. Source

Islam S.M.,Kalyani University | Singha Roy A.,Kalyani University | Mondal P.,Kalyani University | Mondal S.,Kalyani University | And 3 more authors.
Journal of Applied Polymer Science | Year: 2011

Three polymer-anchored metal complexes (Co, Cu, and Pd) were synthesized and characterized. The catalytic performance of these complexes was tested for the oxidation of olefins and aromatic alcohols. These complexes showed excellent catalytic activity and high selectivity. These complexes selectively gave epoxides and aldehydes from olefins and alcohols, respectively. Individually, the effect of various solvents, oxidants, substrate oxidant molar ratios, temperatures, and catalyst amounts for the oxidation of cyclohexene and benzyl alcohol were studied. Under optimized reaction conditions, 96, 81, and 71% conversions of cyclohexene and 86, 79, and 73% conversions of benzyl alcohol were obtained with Co(II), Cu(II), and Pd(II) catalysts, respectively. The catalytic results reveal that these complexes could be recycled more than five times without much loss in activity. © 2011 Wiley Periodicals, Inc. Source

Majumder D.,Santipur College | Majumder D.,Indian Association for The Cultivation of Science | Mandal S.S.,Indian Association for The Cultivation of Science
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We determine the lowest and higher order collective modes in both spin-conserving and spin-reversed sectors by calculating the energy differences of appropriate linear combinations of different levels of the excitons of the composite fermions and the fully spin-polarized ground states at filling factors ν=1/3, 2/5, 3/7, and 4/9. Apart from providing a detailed study of previously reported modes that have also been observed in the experiments, we predict additional higher energy modes at different filling factors. The lowest and the next higher spin-conserving modes have equal number of "magnetorotons" and the number is the same as the number of filled effective Landau-like levels of composite fermions. The higher energy modes at ν=1/3 merge with the lowest mode at long wavelengths. The spin-conserving modes do not merge at other filling factors. Apart from showing a zero-energy spin-wave mode at zero momentum, thanks to Larmor's theorem, the lowest spin-reversed modes at the ferromagnetic ground states of ν=2/5, 3/7, and 4/9 display one or more "spin rotons" at negative energies, signaling unstable fully polarized ground states at sufficiently small Zeeman energies. The high-energy spin-reversed modes also have spin rotons but at positive energies. The energies of these excitations depend on the finite width of the quantum well as the Coulomb interaction gets screened. We perform a finite thickness correction to the Coulomb interaction by the standard method of local density approximation and use it to calculate the critical energies such as rotons and long- and short-wavelength modes, which are detectable in inelastic light scattering experiments. © 2014 American Physical Society. Source

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