Physics

<p>Shiv Nadar University is a comprehensive, multidisciplinary, research-focused, and student-centric University offering a full range of academic programs at the undergraduate, postgraduate and doctoral level. With state-of-the-art infrastructure, the University comprises of academic wings, sophisticated labs, international standard sports facilities, amphitheaters, auditorium, conference rooms and smart classrooms. The University&rsquo;s goal is to become internationally recognized for the quality of its research and creative endeavors and their applicability to improving quality of life, generating new insights and expanding the boundaries of human knowledge creativity. Committed to excellence in teaching, research and service, the University aims to serve the higher education needs of India and the world beyond.</p>

Shiv Nadar University

Several donor (D)-acceptor (A) based molecules are rationally designed by adopting three different schemes in which the conjugation length, strength of the donor and acceptor moieties, and planarity of the molecules are varied. These variations are made by introducing a π-conjugated linkage unit, terminating the ends of the moieties by different electron donating and accepting functional groups, and fusing the donor and acceptor moieties, respectively. Our DFT and TDDFT based calculations reveal that using the above-mentioned design schemes, the electronic and optical properties of the D-A based molecules can be largely tuned. While introduction of a linkage and fusing of moieties enhance the π-π interaction, addition of electron donating groups (-CH3, -OH, and -NH2) and electron accepting groups (-CF3, -CN, -NO2, and -NH3+) varies the strength of the donor and acceptor moieties. These factors lead to modulation of the HOMO and LUMO energy levels and facilitate the engineering of the HOMO-LUMO gap and the optical gap over a wide range of ∼0.7-3.7 eV. Moreover, on the basis of calculated ionization potential and reorganization energy, most of the investigated molecules are predicted to be air stable and to exhibit high electron mobility, with the possibility of the presence of ambipolar characteristics in a few of them. The results of our calculations not only demonstrate the examined molecules to be the potential materials for organic opto-electronic devices, but also establish an understanding of the composition-structure-property correlation, which will provide guidelines for designing and synthesizing new materials of choice. © the Owner Societies 2016.

(SoNS) School of Natural Sciences

Fulltext

Physical Chemistry Chemical Physics

Rationally designed donor-acceptor scheme based molecules for applications in opto-electronic devices

In this paper, effects of lattice strain on dielectric properties of Sr1-xCaxBi2Nb2O9 (x = 0.0-0.5 in steps of 0.1) ceramics are reported. High frequency dipolar polarization is observed to increase for 10\% calcium addition and suppresses thereafter on higher calcium concentrations. The dielectric loss values for all doped samples were lower compared to undoped one at frequencies beyond 1 kHz. The sample with x = 0.1 shows room temperature dielectric constant in the range (130±12) over a wide frequency range from 50 Hz to 1MHz also minimum dielectric loss among all other sample for the same frequeny range. Remarkable increase in Curie temperature (Tc) by 50°C is recorded in the present work by increasing 10\% calcium content in SBN compostion. All higher doped samples indicate increase in Tc by further higher amount. In addition, dc conductivity of all samples is measured for all samples and increase in calcium content is observed to generate more insulating compositions compared to undoped SBN with higher intrinsic activation energies. © The Author(s).

Journal of Advanced Dielectrics

Lattice strain driven dielectric insulation response of Sr1-xCaxBi2Nb2O9 ceramics

Spin-spin correlations and microscopic origin of net magnetization in the spin-1 trimer chain compound CaNi3P4O14 have been investigated by powder neutron diffraction. The present study reveals a three-dimensional long-range magnetic ordering below 16 K where the magnetic structure consists of ferromagnetic trimers that are coupled ferromagnetically along the spin-chain direction (b axis). The moment components along the a and c axes arrange antiferromagnetically. Our study establishes that the uncompensated moment components along the b axis (mb) result in a net magnetization per unit cell. The magnetic structure, determined in the present study, is in agreement with the results of recent first-principles calculation; however, it is in contrast to a fascinating experimental prediction of ferrimagnetic ordering based on the periodicity of the exchange interactions in CaNi3P4O14. Our study also confirms the presence of broad diffuse magnetic scattering, due to one-dimensional short-range spin-spin correlations, over a wide temperature range below ∼50 K down to a temperature well below the Tc. Total neutron scattering analysis by the reverse Monte Carlo (RMC) method reveals that the dominating spin-spin correlation above Tc is ferromagnetic and along the b axis. The nearest-neighbor spin-spin correlations along the a and c axes are found to be weakly antiferromagnetic. The nature of the trimer spin structure of the short-range ordered state (above Tc) is similar to that of the 3D long-range ordered state (below Tc). The present investigation of microscopic nature of the magnetic ground state also explains the condition required for the 1/3 magnetization plateau to be observed in the trimer spin chains. In spite of the S=1 trimer chain system, the present compound CaNi3P4O14 is found to be a good realization of a three-dimensional magnet below Tc=16 K with full ordered moment values of ∼2 $\mu$B/Ni2+ (1.98 and 1.96$\mu$B/Ni2+ for two Ni sites, respectively) at 1.5 K.

World University root node

Physical Review B

Long-range and short-range magnetic correlations and microscopic origin of net magnetization in the spin-1 trimer chain compound CaNi3 P4 O14

We present a doubly parametric extension of the standard Froggatt-Nielsen (FN) mechanism. As is well known, mass matrices of the up- and down-type quark sectors and the charged lepton sector in the standard model can be parametrized well by a parameter λ which is usually taken to be the sine of the Cabibbo angle (λ = sin θc ≃ 0.225). However, in the neutrino sector, there is still room to realize the two neutrino mass squared differences δ m2sol δ m2atm, two large mixing angles θ12 and θ23, and non-zero θ13. Then we consider an extension with an additional parameter p in addition to λ. Taking the relevant FN charges for a power of λ (= 0.225) and additional FN charges for a power of p, which we assume to be less than one, we can reproduce the ratio of the two neutrino mass squared differences and three mixing angles. In the normal neutrino mass hierarchy, we show several patterns for taking relevant FN charges and the magnitude of p. We find that if sin θ23 is measured more precisely, we can distinguish each pattern. This is testable in the near future, for example in neutrino oscillation experiments. In addition, we predict the Dirac CP-violating phase for each pattern. © 2016 The Author(s).

Progress of Theoretical and Experimental Physics

Double froggatt-nielsen mechanism

We investigate a possibility for explaining the recently announced 750 GeV diphoton excess by the ATLAS and CMS experiments at the CERN Large Hadron Collider in a model with multiple doubly charged particles, that was originally suggested for explaining tiny neutrino masses through a three-loop effect in a natural way. The enhanced radiatively generated effective coupling of a new singlet scalar S with diphoton with multiple charged particles in the loop enlarges the production rate of S in pp → S +X via a photon fusion process and also the decay width Γ(S → γ γ ) even without assuming a tree-level production mechanism. We provide detailed analysis on the cases with or without allowing mixing between S and the standard model Higgs doublet. © The Author(s) 2016.

LHC 750 GeV diphoton excess in a radiative seesaw model

In this study, we have designed a compact sample chamber that can achieve accurate and continuous control of the relative humidity (RH) in the vicinity of 100\%. A 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) multilayer can be used as a humidity sensor by measuring its inter-layer repeat distance (d-spacing) via X-ray diffraction. We convert from DOPC d-spacing to RH according to a theory given in the literature and previously measured data of DOPC multilamellar vesicles in polyvinylpyrrolidone (PVP) solutions. This curve can be used for calibration of RH close to 100\%, a regime where conventional sensors do not have sufficient accuracy. We demonstrate that this control method can provide RH accuracies of 0.1 to 0.01\%, which is a factor of 10-100 improvement compared to existing methods of humidity control. Our method provides fine tuning capability of RH continuously for a single sample, whereas the PVP solution method requires new samples to be made for each PVP concentration. The use of this cell also potentially removes the need for an X-ray or neutron beam to pass through bulk water if one wishes to work close to biologically relevant conditions of nearly 100\% RH. © the Owner Societies 2015.

Accurate calibration and control of relative humidity close to 100% by X-raying a DOPC multilayer

Magnetization, P31 nuclear magnetic resonance study and first-principles electronic structure calculations have been performed in the spin-1 trimer chain compound CaNi3(P2O7)2. Two separate spectra arising from magnetically and crystallographically inequivalent P sites are observed. In the ordered state, the resonance lines for both the P sites (P1 and P2) are found to be split into two, which is clear microscopic evidence of the development of two-sublattice AFM order below TM. A nonnegligible contribution of ferromagnetic hyperfine field and dipolar field have also been seen in the ordered state. The first-principles calculations show that the intratrimer (J1) and intertrimer interactions (J2) are of weak ferromagnetic type with the values 2.85 and 1.49 meV, respectively, whereas the interchain interaction (J3) is of strong antiferromagnetic type with a value of 5.63 meV. The anisotropy of the imaginary part of dynamical spin susceptibility around TM along with the exponential decrement of 1/T1 below TM indicate the probable participation of the Ni-3d electron's orbital degrees of freedom in the ferrimagnetic transition. The dominance of orbital fluctuations over the spin fluctuations seems to be responsible for showing low value of the binding energy u of the local spin configuration (estimated from local spin models) and an unusually weak exponent in the power-law behavior of 1/T1 below 50 K, in the paramagnetic state. Electronic structure calculations also reveal the importance of orbital degrees of freedom of Ni-3d moments, which is consistent with our NMR data analysis.

Physical Review B - Condensed Matter and Materials Physics

Magnetism of the spin-trimer compound CaNi3(P2 O7)2: Microscopic insight from combined P 31 NMR and first-principles studies

We study a generalized scheme of Swanson Hamiltonian from a second-derivative pseudo-supersymmetric approach. We discuss plausible choices of the underlying quasi-Hamiltonian and consider the viability of applications to systems like the isotonic oscillator and CPRS potential. © 2015 World Scientific Publishing Company.

International Journal of Modern Physics A

A generalized Swanson Hamiltonian in a second-derivative pseudo-supersymmetric framework

We classify the combinations of parameters which lead three generations of quarks and leptons in the framework of magnetized twisted orbifolds on T2/Z2, T2/Z3, T2/Z4 and T2/Z6 with allowing nonzero discretized Wilson line phases and Scherk-Schwarz phases. We also analyze two actual examples with nonzero phases leading to one-pair Higgs and five-pair Higgses and discuss the difference from the results without nonzero phases studied previously. (Note: this article is registered under preprint number: arXiv:1501.02787 [hep-ph].). © 2015 The Authors.

Nuclear Physics B

Classification of three-generation models on magnetized orbifolds

Towards developing next generation scalable TiO2-based resistive switching (RS) memory devices, the efficacy of 50 keV Ar+-ion irradiation to achieve self-organized nano-channel based structures at a threshold fluence of 5 × 1016 ions/cm2 at ambient temperature is presented. Although x-ray diffraction results suggest the amorphization of as-grown TiO2 layers, detailed transmission electron microscopy study reveals fluence-dependent evolution of voids and eventual formation of self-organized nano-channels between them. Moreover, gradual increase of TiO/Ti2O3 in the near surface region, as monitored by x-ray photoelectron spectroscopy, establishes the upsurge in oxygen deficient centers. The impact of structural and chemical modification on local RS behavior has also been investigated by current-voltage measurements in conductive atomic force microscopy, while memory application is manifested by fabricating Pt/TiO2/Pt/Ti/SiO2/Si devices. Finally, the underlying mechanism of our experimental results has been analyzed and discussed in the light of oxygen vacancy migration through nano-channels. © 2015 AIP Publishing LLC.