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We explore the possibility and potential benefit of rolling a Si2BN sheet into single-walled nanotubes (NTs). Using density functional theory (DFT), we consider both structural stability and the impact on the nature of chemical bonding and conduction. The structure is similar to carbon NTs and hexagonal boron-nitride (hBN) NTs and we consider both armchair and zigzag Si2BN configurations with varying diameters. The stability of these Si$_2$BN NTs is confirmed by first-principles molecular dynamics calculations, by an exothermal formation, an absence of imaginary modes in the phonon spectra. Also, we find the nature of conduction varies semiconducting, from semi-metallic to metallic, reflecting differences in armchair/zigzag-type structures, curvature effects, and the effect of quantum confinement. We present the detailed characterization of how these properties lead to differences in both the bonding nature and electronic structures, Comment: 14 pages, 8 figures

Recently, holey graphene (HG) has successfully synthesized at atomic precision of hole size and shape. This shows interesting physical and chemical properties for energy and environmental applications. Shaping of the pores also transforms semimetallic graphene to semiconductor holey graphene, which opens new door for its use in electronic applications. We systematically investigated the structural, electronic, optical and thermoelectric properties of HG structure using first-principles calculations. HG was found to have a direct band gap with 0.65 eV (PBE functional), 0.95 eV (HSE06 functional) and HSE06 functional is in good agreement with experimental results. For the optical properties, we use single-shot G0W0 calculations by solving the Bethe-Salpeter equation to determining the intralayer excitonic effects. From the absorption spectrum, we obtained the optical gap of 1.28 eV and a week excitonic binding energy of 80 meV. We have found the large values of thermopower of 1662.59 $\mu$V/K and better electronic figure of merit, ZT$_{e}$ as 1.13 from the investigated thermoelectric properties. Our investigations exhibit strong and broad optical absorption in the visible light region, which makes HG monolayer a promising candidate for optoelectronic and thermoelectric applications., Comment: 9 pages, 10 figures

We present the cationic impurity assisted band offset phenomena in NixCd1-xO (x= 0, 0.02, 0.05, 0.1, 0.2, 0.4, 0.8, 1) thin films and further discussed in the light of orbital hybridization modification. Compositional and structural studies revealed that cationic substitution of Cd2+ by Ni2+ ions leads to a monotonic shift in (220) diffraction peak, indicating the suppression of lattice distortion while evolution of local strain with increasing Ni concentration mainly associated to the mismatch in electro-negativity of Cd2+ and Ni2+ ion. In fact, Fermi level pinning towards conduction band minima takes place with increasing Ni concentration at the cost of electronically compensated oxygen vacancies, resulting modification in the distribution of carrier concentration which eventually affects the band edge effective mass of conduction band electrons and further endorses band gap renormalization. Besides that, the appearance of longitudinal optical (LO) mode at 477 cm-1 as manifested by Raman spectroscopy also indicate the active involvement of electron-phonon scattering whereas modification in local coordination environment particularly anti-crossing interaction in conjunction with presence of satellite features and shake-up states with Ni doping is confirmed by X-ray absorption near-edge and X-ray photoelectron spectroscopy studies. These results manifest the gradual reduction of orbital hybridization with Ni incorporation, leading to decrement in the band edge effective mass of electron. Finally, molecular dynamics simulation reflects 13% reduction in lattice parameter for NiO thin film as compared to undoped one while projected density of states calculation further supports the experimental observation of reduced orbital hybridization with increasing Ni concentration., Comment: 44 pages, 15 figures

In the paper, high temperature induced phase transformation in chemically grown CdO thin films has been demonstrated whereas their corresponding electronic origin is further investigated by density functional theory. In particular, cubic rocksalt to hexagonal wurtzite PT in 900 degree centigrade annealed CdO thin films is confirmed by Xray diffraction , consistent with High Resolution Transmission Electron Microscopy. Such high temperature treatment also leads to significant enhancement in optical band gap from 2.2 to 3.2 eV as manifested by UV-Visible spectroscopy. Moreover, atomic force microscopy and scanning electron microscopy clearly evidence the structural evolution via formation of nano-sheet network in wurtzite phased CdO films. Furthermore, Xray Absorption spectra at oxygen k edge revealed a notable shift in inflection point of absorption edge while X-ray Photoelectron spectroscopy of Cd 3d and O 1s suggested the gradual reduction in CdO2 phase with increasing annealing temperature. In addition, different complementary techniques including Rutherford Backscattering, Raman Spectroscopy have also been exploited to understand the aforementioned PT and their structural correlation. Finally, molecular dynamics simulation along with density functional theory calculations suggest that symmetry modification at Brillouin zone boundary provides a succinct signature for such PT in CdO thin film., Comment: 34 pages, 14 figures, submitted to nanoscale

We revisit a non-perturbative formulation leading to a vacuum created gravitational pair of (33)-brane by a Poincare dual higher form U (1) gauge theory on a D4 -brane. In particular, the analysis has revealed a dynamical geometric torsion H 3 for an on-shell Neveu-Schwarz (NS) form on a fat 4-brane. We argue that a D-instanton can be a viable candidate to incorporate the quintessence correction hidden to an emergent (3 + 1)-dimensional brane universe. It is shown that a dynamical non-perturbative correction may be realized with an axionic scalar QFT on an emergent anti 3-brane within a gravitational pair. The theoretical tool provokes thought to believe for an extra instantaneous dimension transverse to our classical brane-universe in an emergent scenario. Interestingly a D-instanton correction, sourced by an axion on an anti 3-brane, may serve as a potential candidate to explain the accelerated rate of expansion of our 3-brane universe and may provide a clue to the origin of dark energy., Comment: 11 pages, Typos corrected and added new citations

Nowdays, multiferroic materials with magnetoelectric coupling have many real-world applications in the fields of novel memory devices. It is challenging is to create multiferroic materials with strongly coupled ferroelectric and ferrimagnetic orderings at room temperature. The single crystal of ferric selenide (Fe3Se4) shows type-II multiferroic due to the coexistence of ferroelectric as well as magnetic ordering at room temperature. We have investigated the lattice instability, electronic structure, ferroelectric, ferrimagnetic ordering and transport properties of ferroelectric metal Fe3Se4. The density of states shows considerable hybridization of Fe-3d and Se-4p states near the Fermi level confirming its metallic behavior. The magnetic moments of Fe cations follow a type-II ferrimagnetic and ferroelectric ordering with a calculated total magnetic moment of 4.25 per unit cell (Fe6Se8). The strong covalent bonding nature of Fe-Se leads to its ferroelectric properties. In addition, the symmetry analysis suggests that tilting of Fe sub-lattice with 3d-t2g orbital ordering is due to the Jahn-Teller (JT) distortion. This study provides further insight in the development of spintronics related technology using multiferroic materials., Comment: This manuscript is under communication

We revisit a non-perturbation theory of quantum gravity in $1.5$ order underlying an emergent gravitational pair of $(4{\bar 4})$-brane with a renewed interest. In particular the formulation is governed by a geometric torsion ${\cal H}_3$ in second order with an on-shell NS form in first order. Interestingly the gravitational pair is sourced by a Kalb-Ramond two form CFT on a $D_5$-brane in $d$$=$$10$ type IIB superstring theory. We show that a generic form theory containing a CFT sector in $d=6$ bulk may be described by a boundary ${\rm AdS}_5$ with a quintessence Q. Analysis reveals that the bulk/boundary duality in emergent gravity can be a potential tool to explore the quintessential cosmology., Comment: 5 pages, 1 figure

We investigate an effective torsion curvature in a second order formalism underlying a two form world-volume dynamics in a $D_5$-brane. In particular, we consider the two form in presence of a background (open string) metric in a $U(1)$ gauge theory. Interestingly the formalism may be viewed via a non-coincident pair of $(D{\bar D})_5$-brane with a global NS two form on an anti brane and a local two form on a brane. The energy-momentum tensor is computed in the six dimensional CFT. It is shown to source a metric fluctuation on a vacuum created pair of $(D{\bar D})_4$-brane at a cosmological horizon by the two form quanta in the gauge theory. The emergent gravity scenario is shown to describe a low energy (perturbative) string vacuum in $6D$ with a (non-perturbative) quantum correction by a lower ($p<5$) dimensional $D_p$ brane or an anti brane in the formalism. A closed string exchange between a pair of $(D{\bar D})_4$-brane, underlying a closed/open string duality, is argued to describe the Einstein vacuum in a low energy limit. We obtain topological de Sitter and Schwarzschild brane universe in six dimensions. The brane/anti-brane geometries are analyzed to explore some of their characteristic and thermal behaviours in presence of the quantum effects. They reveal an underlying nine dimensional type IIA and IIB superstring theories on $S^1$., Comment: 29 pages, 3 figures, minor revision, typos corrected