arXiv subjects

Sharat Chandra

Publications and source records attributed to Sharat Chandra.

26 records · Page 2Linked to original sources

arXiv2010

Superconductivity in Ru substituted BaFe2-xRuxAs2

The occurrence of bulk superconductivity at ~22 K is reported in polycrystalline samples of BaFe2-xRuxAs2 for nominal Ru content in the range of x=0.75 to 1.125. A systematic suppression of the spin density wave transition temperature (TSDW) precedes the appearance of superconductivity in the system. A phase diagram is proposed based on the measured TSDW and superconducting transition temperature (TC) variations as a function of Ru composition. Band structure calculations, indicate introduction of electron carriers in the system upon Ru substitutiom. The calculated magnetic moment on Fe shows a minimum at x=1.0, suggesting that the suppression of the magnetic moment is associated with the emergence of superconductivity. Results of low temperature and high field Mossbauer measurements are presented. These indicate weakening of magnetic interaction with Ru substitution

cond-mat.supr-con↗

arXiv2007

Multi-phonon Raman scattering in GaN nanowires

UV Raman scattering studies show longitudinal optical (LO) mode up to 4th order in wurtzite GaN nanowire system. Frohlich interaction of electron with the long range electrostatic field of ionic bonded GaN gives rise to enhancement in LO phonon modes. Good crystalline quality, as indicated by the crystallographic as well as luminescence studies, is thought to be responsible for this significant observation. Calculated size dependence, incorporating size corrected dielectric constants, of electron-phonon interaction energy agrees well with measured values and also predict stronger interaction energy than that of the bulk for diameter below ~3 nm.

cond-mat.mtrl-sci↗

arXiv2007

Soft modes and NTE in Zn(CN)2 from Raman spectroscopy and first principles calculations

We have studied Zn(CN)2 at high pressure using Raman spectroscopy, and report Gruneisen parameters of the soft phonons. The phonon frequencies and eigen vectors obtained from ab-initio calculations are used for the assignment of the observed phonon spectra. Out of the eleven zone-centre optical modes, six modes exhibit negative Gruneisen parameter. The calculations suggest that the soft phonons correspond to the librational and translational modes of CN rigid unit, with librational modes contributing more to thermal expansion. A rapid disordering of the lattice is found above 1.6 GPa from X-ray diffraction.

cond-mat.mtrl-sci↗

arXiv2005

Electronic structure of Li2Pd3B and Li2Pt3B

Li2Pd3B is known to be superconducting, while the isotypical Li2Pt3B compound is not. Electronic structures of Li2Pd3B and Li2Pt3B have been calculated in order to obtain an insight into this surprising difference, through an analysis of the differences in the band structures. The electronic structures of these systems were obtained using the Full Potential Linear Augmented Plane Wave plus local orbitals (FP-LAPW+lo) method and it was found that four bands cross the Fermi level (EF). Out of these four bands, only two bands contribute significantly to the density of states at the EF. One of these bands is a hole band and the other an electron band. Thus at least a two-band model is required for studying the electronic properties of the Pd and Pt compounds. These two bands are rather narrow and hence the coulombic correlations effects can be significant.

cond-mat.supr-con↗

arXiv2004

Blue luminescence of Au nanoclusters embedded in silica matrix

Photoluminescence study using the 325 nm He-Cd excitation is reported for the Au nanoclusters embedded in SiO2 matrix. Au clusters are grown by ion beam mixing with 100 KeV Ar+ irradiation on Au [40 nm]/SiO2 at various fluences and subsequent annealing at high temperature. The blue bands above ~3 eV match closely with reported values for colloidal Au nanoclusters and supported Au nanoislands. Radiative recombination of sp electrons above Fermi level to occupied d-band holes are assigned for observed luminescence peaks. Peaks at 3.1 eV and 3.4 eV are correlated to energy gaps at the X- and L-symmetry points, respectively, with possible involvement of relaxation mechanism. The blue shift of peak positions at 3.4 eV with decreasing cluster size is reported to be due to the compressive strain in small clusters. A first principle calculation based on density functional theory using the full potential linear augmented plane wave plus local orbitals (FP-LAPW+LO) formalism with generalized gradient approximation (GGA) for the exchange correlation energy is used to estimate the band gaps at the X- and L-symmetry points by calculating the band structures and joint density of states (JDOS) for different strain values in order to explain the blueshift of ~0.1 eV with decreasing cluster size around L-symmetry point.

cond-mat.mtrl-sci↗

arXiv2004

Rietveld refinement and electron density distribution in CuxV2O5

Room temperature powder x-ray diffraction measurements have been carried out on polycrystalline samples of CuxV2O5 with x = 0.33, 0.40, 0.50, 0.55 and 0.60, prepared by solid state reaction in evacuated quartz tubes. All the samples were found to be in single-phase monoclinic structure. Rietveld full profile refinement of the x-ray diffraction data yielded the lattice parameters and fractional atom coordinates. Maximum entropy inversion of the diffraction data was done in order to obtain the variation in the spatial electron density distribution as a function of copper composition. These density maps show progressive positional and charge disorders in the V-O network induced by addition of copper. It is shown that the electrons donated by copper atoms are transferred to the specific vanadium atom sites.

cond-mat.mtrl-sci↗

arXiv2003

Double metal-insulator transitions and MR in La(0.67)Ca(0.33)Mn(1-x)Ru(x)O(3) (x</=0.10): A qualitative understanding in light of possible magnetic phase separation

This paper is in continuation of our previous work on the structural, electrical and magnetic properties of Ru doped La(0.67)Ca(0.33)MnO(3) compounds (Ref.: L.Seetha Lakshmi et.al, J. Magn. Magn. Mater. 257, 195 (2003)). Here we report the results of magnetotransport measurements on La(0.67)Ca(0.33)Mn(1-x)Ru(x)O(3) (0<x< 0.1) compounds in the light of proposed magnetic phase separation.

cond-mat.str-el↗

arXiv2002

Possible Magnetic separation in Ru doped La0.67Ca0.33MnO3

X-ray diffraction, resistivity, ac susceptibility and magnetization studies on La0.67Ca0.33Mn1-xRuxO3 (0 x < 0.1) were carried out. A significant increase in the lattice parameters indicated the presence of mixed valance state of Ru: Ru3+ and Ru4+. The resistivity of the doped compounds exhibited two features: a broad maximum and a relatively sharp peak. While a para to ferromagnetic transition could be observed for the latter peak, no magnetic signal either in ac susceptibility or in magnetization measurements could be observed for the broad maximum. The magnetic moment decreases non linearly from 3.55 to 3 mB over the Ru composition from 0 to 8.5 at.%. Based on the results of the present studies and on existing literature on the Mn-site substituted systems, we argue that a magnetic phase separation occurs in the Ru doped system. While the sharp peak in the resistivity corresponds to Ru4+ enriched region with a ferromagnetic coupling with neighboring Mn ions, the broad peak corresponds to a Ru3+ rich regions, with an antiferromagnetic coupling with neighboring Mn ions.

cond-mat.str-el↗