arXiv subjects

S. K. Singh

Publications and source records attributed to S. K. Singh.

At least 109 records · Page 6Linked to original sources

arXiv2015

Stable Half-Metallic Monolayers of FeCl$_2$

The structural, electronic and magnetic properties of single layers of Iron Dichloride (FeCl$_{2}$) were calculated using first principles calculations. We found that the 1T phase of the single layer FeCl$_{2}$ is 0.17 eV/unit cell more favorable than its 1H phase. The structural stability is confirmed by phonon calculations. We found that 1T-FeCl$_{2}$ possess three Raman-active (130, 179 and 237 cm$^{-1}$) and one Infrared-active (279 cm$^{-1}$) phonon branches. The electronic band dispersion of the 1T-FeCl$_{2}$ is calculated using both GGA-PBE and DFT-HSE06 functionals. Both functionals reveal that the 1T-FeCl$_{2}$ has a half-metallic ground state with a Curie temperature of 17 K.

cond-mat.mtrl-sci↗

arXiv2015

Fast magnetic field annihilation in the relativistic collisionless regime driven by two ultra-short high-intensity laser pulses

The magnetic quadrupole structure formation during the interaction of two ultra-short high power laser pulses with a collisionless plasma is demonstrated with 2.5-dimensional particle-in-cell simulations. The subsequent expansion of the quadrupole is accompanied by magnetic field annihilation in the ultrarelativistic regime, when the magnetic field can not be sustained by the plasma current. This results in a dominant contribution of the displacement current exciting a strong large scale electric field. This field leads to the conversion of magnetic energy into kinetic energy of accelerated electrons inside the thin current sheet.

physics.plasm-ph↗

arXiv2015

GraphAne: From Synthesis to Applications

Atomically thin crystals have recently been the focus of attention in particular after the synthesis of graphene, a monolayer hexagonal crystal structure of carbon. In this novel material class the chemically derived graphenes have attracted tremendous interest. It was shown that although bulk graphite is a chemically inert material, the surface of single layer graphene is rather reactive against individual atoms. So far, synthesis of several graphene derivatives have been reported such as hydrogenated graphene "graphane" (CH), fluorographene (CF) and chlorographene (CCl). Moreover, the stability of bromine and iodine covered graphene were predicted using computational tools. Among these derivatives, easy synthesis, insulating electronic behavior and reversibly tunable crystal structure of graphane make this material special for future ultra-thin device applications. This overview, surveys structural, electronic, magnetic, vibrational and mechanical properties of graphane. We also present a detailed overview of research efforts devoted to the computational modeling of graphane and its derivatives. Furthermore recent progress in synthesis techniques and possible applications of graphane are reviewed as well.

cond-mat.mtrl-sci↗

arXiv2015

Weak Quasielastic Production of Hyperons and Threshold Production of Two Pions

We have studied quasielastic charged current hyperon production induced by $\barν_μ$ on free nucleon and the nucleons bound inside the nucleus and the results are presented for several nuclear targets like $^{40}Ar$, $^{56}Fe$ and $^{208}Pb$. The hyperon-nucleon transition form factors are determined from neutrino-nucleon scattering and semileptonic decays of neutron and hyperons using SU(3) symmetry. The nuclear medium effects(NME) due to Fermi motion and final state interaction(FSI) effect due to hyperon-nucleon scattering have been taken into account. Also we have studied two pion production at threshold induced by neutrinos off nucleon targets. The contribution of nucleon, pion, and contact terms are calculated using Lagrangian given by nonlinear $σ$ model. The contribution of the Roper resonance has also been taken into account. The numerical results for the cross sections are presented and compared with the experimental results from ANL and BNL.

hep-ph↗

arXiv2014

A relativistic mean field study of multi-strange system

We study the binding energies, radii, single-particle energies, spin-orbit potential and density profile for multi-strange hypernuclei in the range of light mass to superheavy region within the relativistic mean field (RMF) theory. The stability of multi-strange hypernuclei as a function of introduced hyperons ($Λ$ and $Σ$) is investigated. The neutron, lambda and sigma mean potentials are presented for light to superheavy hypernuclei. The inclusion of hyperons affects the nucleon, lambda and sigma spin-orbit potentials significantly. The bubble structure of nuclei and corresponding hypernuclei is studied. The nucleon and lambda halo structure are also investigated. A large class of bound multi-strange systems formed from the combination of nucleons and hyperons (n, p, $Λ$, $Σ^+$ and n, p, $Λ$, $Σ^-$) is suggested in the region of superheavy hypernuclei which might be stable against the strong decay. These multi-strange systems might be produced in heavy-ion reactions.

nucl-th↗

arXiv2014

Nuclear medium effects in Drell-Yan process

We study nuclear medium effects in Drell-Yan processes at small target x using quark parton distribution functions and nucleon structure functions for a bound nucleon calculated in a microscopic nuclear model which takes into account the effect of Fermi motion, nuclear binding and nucleon correlations through a relativistic spectral function. The contributions of $π$ and $ρ$ mesons, target mass corrections and nuclear shadowing are also included. The results are compared with the theoretical and experimental results. The model is able to successfully explain the low target x results of E772 and E866 Drell-Yan experiments and is applicable to the forthcoming experimental analysis of E906 Sea Quest experiment at Fermi Lab.

nucl-th↗

arXiv2014

The effect of self interacting isoscalar-vector meson on finite nuclei and infinite nuclear matter

A detailed study is made for the nucleon-nucleon interaction based on relativistic mean field theory in which the potential is explicitly expressed in terms of mass and the coupling constant of the meson fields. A unified treatment for self-coupling of isoscalar-scalar $σ-$, isoscalar-vector $ω$-mesons and their coupling constant are given with a complete analytic form. The present investigation is focused on the effect of self-interacting higher order $σ$ and $ω$ field on nuclear properties. An attempt is made to explain the collapsing stage of nucleon by higher order $ω$-field. Both infinite nuclear matter and the finite nuclear properties are included in the present study to observe the behaviour or sensitivity of this self interacting terms.

nucl-th↗

arXiv2014

Softness of Sn isotopes in relativistic semi-classical approximation

Within the frame-work of relativistic Thomas-Fermi and relativistic extended Thomas-Fermi approximations, we calculate the giant monopole resonance (GMR) excitation energies for Sn and related nuclei. A large number of non-linear relativistic force parameters are used in this calculations. We find that a parameter set is capable to reproduce the experimental monopole energy of Sn isotopes, when its nuclear matter compressibility lies within $210-230$ MeV, however fails to reproduce the GMR energy of other related nuclei. That means, simultaneously a parameter set can not reproduce the GMR values of Sn and other nuclei.

nucl-th↗

arXiv2014

Anatomy of nuclear matter fundamentals

The bridge between finite and infinite nuclear system is analyzed for the fundamental quantities like binding energy, density, compressibility, giant monopole excitation energy and effective mass of both nuclear matter and finite nuclei systems. It is shown quantitatively that by knowing one of the fundamental property of one system one can estimate the same in its counter part, only approximately

nucl-th↗

arXiv2014

Search of double shell closure in the superheavy nuclei using a simple effective interaction

This paper refers to an another attempt to search for spherical double shell closure nu- clei beyond Z=82, N=126. All calculations and results are based on a newly developed approach entitled as simple effective interaction. Our results predict the combination of magic nucleus occurs at N=182 (Z=114,120,126). All possible evidences for the oc- currence of magic nuclei are discussed systematically. And, the obtained results for all observables compared with the relativistic mean field theory for NL3 parameter.

nucl-th↗

arXiv2014

$Λ-$hyperon interaction with nucleons

We study the interaction of $Λ-$hyperon with proton and neutron inside a nucleus within the framework of relativistic mean field formalism. The single particle energy levels for some of the specific proton and neutron orbits are analyzed with the addition of $Λ-$successively. We found that the interaction of $Λ$ with neutron is more stronger than proton.

nucl-th↗

arXiv2014

Effects of isovector scalar $δ$-meson on hypernuclei

We analyze the effects of $δ-$ meson on hypernuclei within the frame-work of relativistic mean field theory. The $δ-$ meson is included into the Lagrangian for hypernuclei. The extra nucleon-meson coupling ($g_δ$) affects the every piece of physical observables, like binding energy, radii and single particle energy of hypernuclei. The lambda mean field potential is investigated which is consistent with other predictions. Flipping of single particle energy levels are observed with the strength of $g_δ$ in the considered hypernuclei as well as normal nuclei. The spin-orbit potentials are observed for considered hypernuclei and the effect of $g_δ$ on spin-orbit potentials is also analyzed. The calculated single-$Λ$ binding energies ($B_Λ$) are quite agreeable with the experimental data.

nucl-th↗

arXiv2013

Weak Strangeness and Eta Production

We have studied strange particle production off nucleons through $ΔS =0 $ and $|ΔS| = 1$ channels, and specifically single kaon/antikaon, eta, associated particle production for neutrino/antineutrino induced processes as well as antineutrino induced single hyperon production processes. We have developed a microscopical model based on the SU(3) chiral Lagrangians. The basic parameters of the model are $f_π$, the pion decay constant, Cabibbo angle, the proton and neutron magnetic moments and the axial vector coupling constants for the baryons octet. For antikaon production we have also included $Σ^*(1385)$ resonance and for eta production $S_{11}(1535)$ and $S_{11}(1650)$ resonances are included.

hep-ph↗

arXiv2013

${\barν}_l$ induced pion production from nuclei at $\sim$1 GeV

We have studied charged current $\barν_l$ induced one pion production from $^{12}$C and $^{16}$O nuclear targets at MiniBooNE and atmospheric antineutrino energies. The calculations have been done for the incoherent pion production process as well as for the pions coming from the hyperons in the quasielastic production of $Λ$ and $Σ$. The calculations are done in the local density approximation. For the inelastic processes the calculations have been done in the $Δ$ dominance model and we take into account the effect of Pauli blocking, Fermi motion of the nucleon and renormalization of $Δ$ properties in the nuclear medium. The effect of final state interaction(FSI) of pions is also taken into account. For the hyperon production, the nuclear medium effects due to Fermi motion and FSI effects due to hyperon-nucleon scattering have been taken into account. These results may be quite useful in the analysis of SciBooNE, MicroBooNE, MINER$ν$A, and ArgoNeuT experiments when the pion analysis is done by using antineutrino beams.

nucl-th↗

arXiv2013

Spiral graphone and one sided fluorographene nano-ribbons

The instability of a free-standing one sided hydrogenated/fluorinated graphene nano-ribbon, i.e. graphone/fluorographene, is studied using ab-initio, semiempirical and large scale molecular dynamics simulations. Free standing semi-infinite arm-chair like hydrogenated/fluorinated graphene (AC-GO/AC-GF) and boat like hydrogenated/fluorinated graphene (B-GO/B-GF) (nano-ribbons which are periodic along the zig-zag direction) are unstable and spontaneously transform into spiral structures. We find that rolled, spiral B-GO and B-GF are energetically more favorable than spiral AC-GO and AC-GF which is opposite to the double sided flat hydrogenated/fluorinated graphene, i.e. graphane/fluorographene. We found that the packed, spiral structures exhibit unexpected localized HOMO-LUMO at the edges with increasing energy gap during rolling. These rolled hydrocarbon structures are stable beyond room temperature up to at least $T$=1000\,K.

cond-mat.mes-hall↗

arXiv2013

Thermal properties of fluorinated graphene

Large scale atomistic simulations using the reactive force field approach (ReaxFF) are implemented to investigate the thermomechanical properties of fluorinated graphene (FG). A new set of parameters for the reactive force field potential (ReaxFF) optimized to reproduce key quantum mechanical properties of relevant carbon-fluor cluster systems are presented. Molecular dynamics (MD) simulations are used to investigate the thermal rippling behavior of FG and its mechanical properties and compare them with graphene (GE), graphane (GA) and a sheet of BN. The mean square value of the height fluctuations $< h^2>$ and the height-height correlation function $H(q)$ for different system sizes and temperatures show that FG is an un-rippled system in contrast to the thermal rippling behavior of graphene (GE). The effective Young's modulus of a flake of fluorinated graphene is obtained to be 273 N/m and 250 N/m for a flake of FG under uniaxial strain along arm-chair and zig-zag direction, respectively.

cond-mat.mes-hall↗

arXiv2013

Ground state properties and bubble structure of superheavy nuclei

We calculate the ground state properties of recently synthesized superheavy nuclei starting from $Z$=105-120. The nonrelativistic and relativistic mean field formalisms is used to evaluate the binding energy, charge radius, quadrupole deformation parameter and the density distribution of nucleons. We analyzed the stability of the nuclei based on the binding energy and neutron to proton ratio. We also studied the bubble structure of the nucleus which reveals about the special features of the superheavy nucleus.

nucl-th↗

arXiv2013

Relativistic mean field study of 'islands of inversion' in neutron rich Z = 17 - 23, 37 - 40 and 60 - 64 nuclei

We study the extremely neutron-rich nuclei for $Z = 17 - 23$, $37 - 40$ and $60 - 64$ regions of the periodic table by using axially deformed relativistic mean field formalism with NL3* parametrization. Based on the analysis of binding energy, two neutron separation energy, quadrupole deformation and root mean square radii, we emphasized the speciality of these considered regions which are recently predicted islands of inversion.

nucl-th↗