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

Carbon ion implantation mediated blue photoluminescence (PL) and the corresponding bluish white phosphorescence of anodic aluminum oxide (AAO) are presented. In particular, the observed 465 nm luminescence is found to be more sensitive to carbon, while its lifetime is raised to its maximum from 6.7 to 10.4 μs at a fluence of 1 × 106ions/cm The observed phenomenon seems to be associated with the formation of oxygen vacancy (V0) via carbon ion enhanced modification of local AlO6 octahedral symmetry, as revealed from X-ray absorption spectroscopy at O-K edge, and also consistent with X-ray photoelectron spectroscopy (XPS). Detailed XPS analysis indicates the preference of carbon at the Al sites, rather than at O for both octahedral and tetrahedral structures, and form CAl cationic impurity, consistent with our density functional theory calculation. Further, carbon ion implantation driven enhanced PL lifetime is shown to be associated with energy transfer between V0 and the vicinal CAl. This work shows the potential of carbon doped AAO as a future candidate for developing rare earth free nontoxic phosphor. © 2019 Author(s).

(SoNS) School of Natural Sciences

Fulltext

Journal of Applied Physics

Revealing carbon mediated luminescence centers with enhanced lifetime in porous alumina

A number of experimental anomalies involving neutrinos hint towards the existence of at least an extra (a very light) sterile neutrino. However, such a species, appreciably mixing with the active neutrinos, is disfavored by different cosmological observations like Big Bang Nucleosynthesis (BBN), Cosmic Microwave Background (CMB) and Large Scale Structure (LSS). Recently, it was shown that the presence of additional interactions in the sterile neutrino sector via light bosonic mediators can make the scenario cosmologically viable by suppressing the production of the sterile neutrinos from active neutrinos via matter-like effect caused by the mediator. This mechanism works assuming the initial population of this sterile sector to be negligible with respect to that of the Standard Model (SM) particles, before the production from active neutrinos. However, there is fair chance that such bosonic mediators may couple to the inflaton and can be copiously produced during (p)reheating epoch. Consequently, they may ruin this assumption of initial small density of the sterile sector. In this article we, starting from inflation, investigate the production of such a sterile sector during (p)reheating in a large field inflationary scenario and identify the parameter region that allows for a viable early Universe cosmology.

World University root node

European Physical Journal C

Inflation, (p)reheating and neutrino anomalies: production of sterile neutrinos with secret interactions

We perform a comprehensive dark matter analysis of left-right supersymmetric scenarios that includes constraints from dark matter direct and indirect detection experiments and that presents distinctive features from those available in minimal supersymmetry. We concentrate on dark matter candidates which, while satisfying all constraints, are different from those of the minimal supersymmetric standard model. We consider in our analysis all possible co-annihilation channels relevant for setups in which several states are light and nearly degenerate and devise a set of representative benchmark points, requiring co-annihilations, which satisfy all restrictions. We then study their consequent LHC signals, which exhibit promising new multileptonic signatures involving WR, that if observed, would provide a strong support for left-right supersymmetry.

Physical Review D

Multileptonic signals of co-annihilating left-right supersymmetric dark matter

Detailed magnetization, specific heat and Li7 nuclear magnetic resonance (NMR) measurements on single crystals of the hyperhoneycomb Kitaev magnet $\beta$-Li2IrO3 are reported. At high temperatures, anisotropy of the magnetization is reflected by the different Curie-Weiss temperatures for different field directions, in agreement with the combination of a ferromagnetic Kitaev interaction (K) and a negative off-diagonal anisotropy ($\Gamma$) as two leading terms in the spin Hamiltonian. At low temperatures, magnetic fields applied along a or c have only a weak effect on the system and reduce the N{\'{e}}el temperature from 38 K at 0 T to about 35.5 K at 14 T, with no field-induced transitions observed up to 58 T on a powder sample. In contrast, the field applied along b causes a drastic reduction in the TN that vanishes around Hc=2.8T, giving way to a crossover toward a quantum paramagnetic state. Li7 NMR measurements in this field-induced state reveal a gradual line broadening and a continuous evolution of the line shift with temperature, suggesting the development of local magnetic fields. The spin-lattice relaxation rate shows a peak around the crossover temperature 40 K and follows power-law behavior below this temperature.

Physical Review Materials

Anisotropic temperature-field phase diagram of single crystalline $\beta$-Li2IrO3: Magnetization, specific heat and Li 7 NMR study

In this work we have considered a minimal extension of Standard Model by a local U(1) gauge group in order to accommodate a stable (fermionic) Dark Matter (DM) candidate. We have focussed on parameter regions where DM possesses adequate self-interaction, owing to the presence of a light scalar mediator (the dark Higgs), alleviating some of the tensions in the small-scale structures. We have studied the scenario in the light of a variety of data, mostly from dark matter direct searches, collider searches and flavor physics experiments, with an attempt to constrain the interactions of the standard model (SM) particles with the ones in the Dark Sector (DS). Assuming a small gauge kinetic mixing parameter, we find that for rather heavy DM the most stringent bound on the mixing angle of the Dark Higgs with the SM Higgs boson comes from dark matter direct detection experiments, while for lighter DM, LHC constraints become more relevant. Note that, due to the presence of very light mediators, the effective operator approach to the direct detection is inapplicable here and these constraints have been re-evaluated for our scenario. In addition, we find that the smallness of the relevant portal couplings, as dictated by data, critically suppress the viability of DM production by the standard “freeze-out” mechanism in such simplified scenarios. In particular, the viable DM masses are ≲ O(2) GeV i.e. in the regions where direct detection limits tend to become weak. For heavier DM with large self-interactions, we hence conclude that non-thermal production mechanisms are favored. Lastly, future collider reach of such a simplified scenario has also been studied in detail.

Journal of High Energy Physics

Scope of self-interacting thermal WIMPs in a minimal U(1)D extension and its future prospects

The possibilities of precise control over the wetting characteristics of carbon-based hybrid nanostructures consisting of both sp2 and sp3 hybridized carbons using the electrowetting technique were demonstrated. An excellent polarity-dependent electrowetting behavior in the presence of an electrolyte followed an abrupt transition from the highly hydrophobic (contact angle ∼ 142°) Cassie-Baxter states to a hydrophilic (∼30°) Wenzel state, where diamond films acted as the anode. In addition, we also reported a remarkable transition from weakly hydrophobic to nearly superhydrophobic diamond nanostructures by chemical and morphological manipulations. The unique structural properties with precisely tailored morphology and surface roughness enabled such transitions on the nanostructured surface. This approach of preparing environmental stable hydrophobic surfaces with polarity-dependent wetting and precise control of the wetting mode transition could be used in numerous applications such as the electrochemical transport of liquids, supercapacitors, and low-friction microfluidics. © 2019 The Royal Society of Chemistry.

Journal of Materials Chemistry A

Direct synthesis of electrowettable nanostructured hybrid diamond

MassiveMIMO(MaMI) is one of the fiery topics in 5G wireless communications. It is introduced based on the fact that the channel vectors becomes asymptotically orthogonal (as antenna elements tending to infinity). Convergence of frequency selective channel (quasi static block fading) characteristics in terms of favorable propagation and channel hardening (asymptotically orthogonal) conditions are studied using metrics like Eigenvalue Ratio (EVR), Mean Absolute Deviation (MAD) and Diagonal Dominance (DD). Finally, simulations results for convergence metrics EVR, MAD and DD are compared with its limiting behavior. The effect of time delay spread on the channel convergence is studied based on the condition number of channel matrix. © 2019 IEEE.

Electrical Engineering

(SoE) School of Engineering

IEEE Region 10 Annual International Conference, Proceedings/TENCON

Convergence of MassiveMIMO Frequency Selective Channels

The mechanisms, extent, and rate of K-storage in graphenic and graphitic carbons, as direct comparisons with Li-storage in the same structures/materials, in terms of the effects of dimensional scale and presence of surface and exposed edge sites have been brought to the fore via DFT-based simulations, duly complemented and supplemented by experimental studies. The simulation indicates feasibilities toward K-storage on single-layer graphene (SLG) at a concentration greater than that in graphite (i.e., beyond KC8), the formation of more than one layer of K on SLG, and K-storage on both the surfaces of SLG, unlike that for Li-storage. Simulations done with graphene nanoribbons (GNRs) indicate that K can get hosted on the graphene surfaces and at the exposed "stepped" edges, in addition to the "classical" K-intercalation in-between the constituent graphene layers. Accordingly, the computation studies indicate considerably enhanced K-storage "specific capacity" of GNR, as compared to bulk graphite, with the capacity decreasing with the increase in number of graphene layers. Electrochemical potassiation/depotassiation of well-ordered fairly pristine few layers graphene films (FLG; ∼6-7 layers) confirms the simultaneous occurrences of bulk (i.e., K-intercalation) and surface storage of K, resulting in reversible K-storage capacity being greater than that of thicker bulk graphite films by a factor of ∼2.5. This is in agreement with the predictions from DFT. However, this increment is less compared to that for Li-storage, again in accordance with the DFT results. Our measurements indicate lower diffusivity of K, as compared to Li, in the same graphitic structure by an order of magnitude. Accordingly, the rate capability of K-storage in graphite has been found to be considerably inferior to Li-storage, which renders the reduction in dimensional scale even more important in the case of K-storage, as observed here with FLG. © 2019 American Chemical Society.

ACS Nano

Enhanced and faster potassium storage in graphene with respect to graphite: A comparative study with lithium storage

Benchmark scenarios for LRSUSY dark matter studies

In this work, layered perovskite SBN was investigated in a new-doped form for hole as well as electron transport layer (HTL/ETL) in perovskite solar cells. This work was targeted to determine utility of bismuth layer SBN materials as an active layer in hybrid perovskite solar cells. Thoroughly hard ball-milled compositions Sr1−xSnxBi1.95La0.05Nb2O9 (x = 0.0, 0.01, 0.03, 0.05, 0.1 and 0.2) were prepared by microwave synthesis to obtain fine (~ 10–60 nm) mesoporous particle network of atomic level substitutions. Microwave synthesis was crucial in modifying dielectric, semiconducting and optical characteristics of prepared SBN materials. The optical energy band gap and hall resistivity decreased in continuous manner on tin doping. The role of metallic tin as dopant in sharpening redox peaks and decreasing capacitive reactance of grain boundaries was investigated in detail using cyclic voltammetry and impedance spectroscopy respectively. The tin being more polar covalent than strontium augmented dielectric response too. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.