arXiv subjects

A. Bhattacharya

Publications and source records attributed to A. Bhattacharya.

At least 109 records · Page 6Linked to original sources

arXiv2011

Strain induced band gap deformation of H/F passivated graphene and h-BN sheet

Strain induced band gap deformations of hydrogenated/fluorinated graphene and hexagonal BN sheet have been investigated using first principles density functional calculations. Within harmonic approximation, the deformation is found to be higher for hydrogenated systems than for the fluorinated systems. Interestingly, our calculated band gap deformation for hydrogenated/fluorinated graphene and BN sheets are positive, while those for pristine graphene and BN sheet are found to be negative. This is due to the strong overlap between nearest neighbor π orbitals in the pristine sheets, that is absent in the passivated systems. We also estimate the intrinsic strength of these materials under harmonic uniaxial strain, and find that the in-plane stiffness of fluorinated and hydrogenated graphene are close, but larger in magnitude as compared to those of fluorinated and hydrogenated BN sheet.

cond-mat.mtrl-sci↗

arXiv2010

Cation-ordering effects in the single layered manganite La(2/3)Sr(4/3)MnO4

We have synthesized epitaxial La(1-x)Sr(1+x)MnO4 (x=1/3) films as random alloys and cation-ordered analogues to probe how cation order affects the properties of a 2D manganite. The films show weak ferromagnetic ordering up to 130 K, although there is a dramatic difference in magnetic anisotropy depending on the cation order. While all films exhibit similar gapped insulator behavior above 130 K, there is a significant difference in the low temperature transport mechanism depending on the cation order. Differences in magnetic anisotropy and low temperature transport are consistent with differences in Mn 3d orbital occupancies. Together this work suggests that cation ordering can significantly alter the Mn 3d orbital ground state in these correlated electron systems.

cond-mat.str-el↗

arXiv2010

Nucleon in Nuclear Matter

The modification of the properties of nucleon in nuclear medium have been investigated in the context of flux tube model. A nucleon has been described as diquark-quark system connected by flux tube and quasi particle diquark model has been used to describe the diquak constituting the nucleon. The modification of incompressiblity, the roper resonance etc in the nuclear medium have been investigated. The results are compared with recent experimental and theoretical predictions.

hep-ph↗

arXiv2010

The third conformer of graphane: A first principles DFT based study

We propose, on the basis of our first principles density functional based calculations, a new isomer of graphane, in which the C-H bonds of a hexagon alternate in 3-up, 3-down fashion on either side of the sheet. This 2D puckered structure called 'stirrup' has got a comparable stability with the previously discovered chair and boat conformers of graphane. The physico-chemical properties of this third conformer are found to be similar to the other two conformers of graphane with an insulating direct band gap of 3.1 eV at the Γ point. Any other alternative hydrogenation of the graphene sheet disrupts its symmetric puckered geometry and turns out to be energetically less favorable.

cond-mat.mtrl-sci↗

arXiv2010

Electronic and Structural Analysis of a Stable Hydrogenated BN sheet (BHNH): A First Principles Based Approach

From first-principles density functional calculations, we study the structural and electronic properties of a stable hydrogenated BN sheet, having formula unit BHNH. In the optimized BHNH structure, the H atoms stabilize on the B and N sites, alternating themselves on both sides of the BN-plane in specific periodic manner, giving rise to different BHNH conformers, viz. chair, boat and stirrup. The chair and boat conformers resemble in structure to those of graphane (CH). We propose a new conformer, called 'stirrup' conformer, that turns out to be the most stable, albeit marginally with respect to the boat conformer. All these BHNH conformers are insulator, with band gap varying between ~ 3.0 eV to 4.5 eV.

cond-mat.mtrl-sci↗

arXiv2010

On the Nature of the Rapidity-Spectra at RHIC and Some Other Energies

On the basis of the Grand Combinational Model (GCM) outlined and somewhat detailed in the text, we have attempted to capture here the several interesting assorted characteristics of the rapidity-spectra of the major varieties of secondaries produced in diverse nuclear reactions at various energies, though the main thrust of our work lies on addressing the data-trends from RHIC-BNL experiments. Obviously the core of the present approach is purely phenomenological. Still, the method and the model address the features of the data modestly well. And the method appears to have the rich potentiality, if the systematic sets of data for rapidity-studies at gradually increasing energies were available.

hep-ph↗

arXiv2010

Quantifying octahedral rotations in strained perovskite oxide films

Epitaxial strain is a proven route to enhancing the properties of complex oxides, however, the details of how the atomic structure accommodates strain are poorly understood due to the difficulty of measuring the oxygen positions in thin films. We present a general methodology for determining the atomic structure of strained oxide films via x-ray diffraction, which we demonstrate using LaNiO3 films. The oxygen octahedral rotations and distortions have been quantified by comparing the intensities of half-order Bragg peaks, arising from the two unit cell periodicity of the octahedral rotations, with the calculated structure factor. Combining ab initio density functional calculations with these experimental results, we determine systematically how strain modifies the atomic structure of this functional oxide.

cond-mat.mtrl-sci↗

arXiv2010

Understanding the New High Energy Data-sets Measured by BESS, CAPRICE and PAMELA on Antiproton Flux and $\bar{P}/P$ Ratios

Reliable data from the very recent high-precision measurements on the antiproton fluxes and the antiproton-to-proton ratios by the PAMELA Collaboration at relatively much higher energies are now available. The results with regard to antiproton production phenomena spring no special surprises; rather they are sharply in contrast with and contradiction to the case of positron production at the same energy-range. However, the totality of data on antiproton production from the past experiments to the very recent PAMELA outburst seem to be a very challenging exercise for interpretation in terms of the secondary production mechanisms alone, the galactic propagation model etc against the background of the `dark-matter'-related controversy. In the present work we assume the validity of the simple leaky box model, choose a simple particle production model and attempt at providing a comprehensive interpretation of the totality of data on both antiproton flux measurements and the $\overline{P}/P$ ratio-values for the various experiments ranging from BESS, CAPRICE to the latest PAMELA experiment. With the assumption of no contribution from the exotic sources to the antiproton production process, our model and the method describe the totality of the measured data with a fair degree of success.

astro-ph.HE↗

arXiv2009

Onset of metallic behavior in strained (LaNiO3)n/(SrMnO3)2 superlattices

(LaNiO3)n/(SrMnO3)2 superlattices were grown using ozone-assisted molecular beam epitaxy. In situ reflection high energy electron diffraction and x-ray scattering has been used to characterize the structural properties of the superlattices, which are strained to the SrTiO3 substrates. The superlattices exhibit excellent crystallinity and interfacial roughness of less than one unit cell. A metal-insulator transition is observed as $n$ is decreased from 4 to 1. Analysis of the transport data suggests an evolution from gapped insulator (n=1) to hopping conductor (n=2) to metal (n=4) with increasing LaNiO3 concentration.

cond-mat.mtrl-sci↗

arXiv2008

Temperature Dependent Structure Function Of Nucleon

A relation between temperature, Fermi momentum and radius of the nucleon has been derived. The percentage increase in radii of the nucleon with temperature and the temperature dependent F$_{2}$ structure function of the nucleon have been investigated. An estimate of the Fermi momentum of the nucleon has been made. The results are found to be in agreement with existing theoretical and experimental suggestions .

hep-ph↗

arXiv2008

A Study on the Structure Functions and the radius of the Nucleons

We have investigated the properties of the structure functions of the nucleons in the context of the statistical model using only the radius parameter of the respective nucleons. The radius of the neutron has been estimated and is found to be 0.8fm. It is interesting to observe that the proton radius 0.865fm which exactly equals to the most accepted charge radius of the proton and which in turn characterizes proton as a meso object, yields reasonable results for the structure function and its properties. GT sum rule has been investigated with some interesting conclusions.

hep-ph↗

arXiv2008

Magnetically asymmetric interfaces in a (LaMnO$_3$)/(SrMnO$_3$) superlattice due to structural asymmetries

Polarized neutron reflectivity measurements of a ferromagnetic [(LaMnO$_3$)$_{11.8}$/(SrMnO$_3$)$_{4.4}$]$_6$ superlattice reveal a modulated magnetic structure with an enhanced magnetization at the interfaces where LaMnO$_3$ was deposited on SrMnO$_3$ (LMO/SMO). However, the opposite interfaces (SMO/LMO) are found to have a reduced ferromagnetic moment. The magnetic asymmetry arises from the difference in lateral structural roughness of the two interfaces observed via electron microscopy, with strong ferromagnetism present at the interfaces that are atomically smooth over tens of nanometers. This result demonstrates that atomic-scale roughness can destabilize interfacial phases in complex oxide heterostructures.

cond-mat.mtrl-sci↗

arXiv2007

The metal-insulator transition and its relation to magnetic structure in (LaMnO3)2n/(SrMnO3)n superlattices

Superlattices of (LaMnO3)2n/(SrMnO3)n (n=1 to 5), composed of the insulators LaMnO3 and SrMnO3, undergo a metal-insulator transition as a function of n, being metallic for n<=2 and insulating for n>=3. Measurements of transport, magnetization and polarized neutron reflectivity reveal that the ferromagnetism is relatively uniform in the metallic state, and is strongly modulated in the insulating state, being high in LaMnO3 and suppressed in SrMnO3. The modulation is consistent with a Mott transition driven by the proximity between the (LaMnO3)/(SrMnO3) interfaces. Disorder localizes states at the Fermi level at the interfaces for n>=3. We suggest that this disorder is due to magnetic frustration at the interfaces.

cond-mat.str-el↗

arXiv2007

Viscous spin exchange torque on precessional magnetization in $(\mathrm{LaMnO}_3)_{2n}/(\mathrm{SrMnO}_3)_{n}$ superlattices

Photoinduced magnetization dynamics is investigated in chemically ordered $(\mathrm{LaMnO}_3)_{2n}/(\mathrm{SrMnO}_3)_n$ superlattices using the time-resolved magneto-optic Kerr effect. A monotonic frequency-field dependence is observed for the $n=1$ superlattice, indicating a single spin population consistent with a homogeneous hole distribution. In contrast, for $n\geq2$ superlattices, a large precession frequency is observed at low fields indicating the presence of an exchange torque in the dynamic regime. We propose a model that ascribes the emergence of exchange torque to the coupling between two spin populations -- viscous and fast spins.

cond-mat.mtrl-sci↗

arXiv2006

On some properties of Exotic Baryons in Quasi particle diquark model

The properties of the Theta^{+} and Xi^{--}_{3/2} exotic baryons have been investigated in the framework of diquark- diquark-antiquark system. A model for diquark suggested in an analogy with the quasi-particle in a crystal lattice has been used. The mass of the exotics have been computed. The Decay width of the Theta^{+} has been estimated to be ~ 11 MeV using effective diquark theory. The radius of the Xi^{--}_{3/2} has been extracted as 0.94fm using the experimental value of the frac{Γ_{Θ^{+}}}{Γ_{Ξ^{--}_{3/2}}}. The results obtained are found to be in good agreement with the present experimental and theoretical suggestions.

hep-ph↗

arXiv2006

Properties of proton in diquark model

The properties of the proton has been investigated considering a proton as diquark-quark system. A model for diquark has been suggested in an analogy with the quasi-particle in a crystal lattice. The mass of the diquark obtained in the present model has been found to be in good agreement with other theoretical predictions. The binding energy of proton, compressibility and excitation energy for the Roper Resonance have also been estimated in the present model and are found to be in agreement with the existing theoretical and experimental findings.

hep-ph↗

arXiv2006

A Study on the structure of proton

The structure function of the proton has been investigated and has been found to possess the power law behaviour in conformity with the empirical fits to the experimental findings. We have estimated F$_{2}$(x, Q$^{2}$)/F$_{2}$(x, Q$_{0}$$^{2}$) with the anomalous dimension D$_{A}$ predicted from the statistical model as an input and the result is found to be in good agreement with the recent data available in the deep inelastic region.

hep-ph↗

arXiv2005

Electrostatic Tuning of the Superconductor-Insulator Transition in Two Dimensions

Superconductivity has been induced in insulating ultra-thin films of amorphous bismuth using the electric field effect. The screening of electron-electron interaction was found to increase with electron concentration in a manner correlated with the tendency towards superconductivity. This does not preclude an increase in the density of states being important in the development of superconductivity. The superconductor-insulator transition appears to belong to the universality class of the three dimensional XY model.

cond-mat.supr-con↗