Department of Physics

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We study the behavior of the exchange bias (EB) and the blocking temperature in an antiferromagnetic FeVO 4 –ferrimagnetic Fe 3 O 4 nanocomposite system upon annealing in Ar atmosphere. Surprisingly, the blocking temperature of post-annealed samples increased to ∼ 50 K, more than two-fold compared the Néel temperature (T N = 22 K) of individual FeVO 4 nanoparticles. This significant enhancement of the blocking temperature was accompanied by the corresponding increase of EB, from ∼ 50 Oe in as-prepared samples to ∼ 110 Oe in post-annealed samples. The temperature dependence of EB can be described by two approximately linear regions with different slopes, with an inflection point at T ∼ 21 K coinciding with the Néel temperature of FeVO 4 nanoparticles. The region above the inflection point with non-zero EB is characterized by a weaker temperature dependence and is expanded well beyond T N . The x-ray photoemission spectroscopy measurements indicate that the surface of post-annealed Fe 3 O 4 particles becomes oxygen deficient, which leads to a modification of the electronic, magnetic and morphological properties of the FeVO 4 /Fe 3 O 4 interface. We associate this unusual behavior with a magnetic proximity effect, in which the ordering temperature of the antiferromagnetic FeVO 4 nanoparticles and the corresponding exchange bias are strongly affected by the adjacent ferrimagnetic Fe 3 O 4 layer. © 2019, The Minerals, Metals & Materials Society.

World University root node

Journal of Electronic Materials

Exchange Bias Enhancement and Magnetic Proximity Effect in FeVO 4 -Fe 3 O 4 Nanoparticles

A three-level atom in Λ configuration is reduced to an effective two-level system, under appropriate conditions, and its PT symmetric properties are investigated. This effective qubit system, when subjected to a beam-splitter type of interaction, provides the scope of directly (indirectly) probing the nonclassical properties of the output (input) state. Here, we study nonclassical properties of the output state by using some well-known measures of nonclassical correlations like the measurement-induced disturbance, concurrence, and negativity. The nonclassical features are found to enhance in the PT symmetric (PTS) phase compared to the PT symmetry broken (PTB) phase. Further, the output ports of the beam splitter are subjected to different quantum noise channels, both non-Markovian, e.g., random telegraph noise as well as Markovian, e.g., phase damping and amplitude damping noise. The application of noise channels is found to decrease the degree of nonclassicality, though continuing to exhibit distinct behavior in PTS and PTB phases, with the dominant behavior appearing in the former case. Further, the results are compared with the case when dynamics is governed by a Hermitian Hamiltonian. This allows one to demarcate the contributions to nonclassicality from different types of dynamics. © 2019 American Physical Society. ©2019 American Physical Society.

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Physical Review A

Interplay between nonclassicality and PT symmetry in an effective two-level system with open system effects

We study the interplay between coherence and mixedness in meson and neutrino systems. The dynamics of the meson system is treated using the generic decoherence model taking into account the decaying nature of the system. Neutrino dynamics is studied in the context of three flavour oscillations within the framework of a decoherence model recently used in the context of LSND (Liquid Scintillator Neutrino Detector) experiment. For meson systems, the decoherence effect is negligible in the limit of zero CP violation. Interestingly, the average mixedness increases with time for about one lifetime of these particles. For neutrino system, in the context of the model considered, the decoherence effect is maximum for neutrino energy around 30 MeV. Further, the effect of CP violating phase is found to decrease (increase) the coherence in the upper 0 &lt; δ&lt; π (lower π&lt; δ&lt; 2 π) half plane. © 2019, The Author(s).

European Physical Journal C

Study of coherence and mixedness in meson and neutrino systems

Covalent organic frameworks (COFs) have garnered immense scientific interest among porous materials because of their structural tunability and diverse properties. However, the response of such materials toward laser-induced nonlinear optical (NLO) applications is hardly understood and demands prompt attention. Three novel regioregular porphyrin (Por)-based porous COFs—Por-COF-HH and its dual metalated congeners Por-COF-ZnCu and Por-COF-ZnNi—have been prepared and present excellent NLO properties. Notably, intensity-dependent NLO switching behavior was observed for these Por-COFs, which is highly desirable for optical switching and optical limiting devices. Moreover, the efficient π-conjugation and charge-transfer transition in ZnCu-Por-COF enabled a high nonlinear absorption coefficient (β=4470 cm/GW) and figure of merit (FOM=σ1/σo, 3565) value compared to other state-of-the-art materials, including molecular porphyrins (β≈100–400 cm/GW), metal–organic frameworks (MOFs; β≈0.3–0.5 cm/GW), and graphene (β=900 cm/GW). © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Angewandte Chemie - International Edition

Nonlinear Optical Switching in Regioregular Porphyrin Covalent Organic Frameworks

Optics InfoBase Conference Papers

Nonlinearity controlled asymmetric mode-conversion in an optical waveguide hosting an exceptional point

We study optical pulse propagation through a linear, dispersive, gain-loss-assisted bulk medium whose refractive index is time-varying. To analyze the dynamics, we have used a novel technique of time transformation that provides universal formulas of pulse propagation. Our analytical and numerical investigations reveal that optical pulses show asymmetric behavior while propagating in opposite direction through such a medium, in both the temporal and spectral domains. Moreover, the wavelength shift during this process is the most interesting outcome which is limited in range, but could be tuned by varying the refractive index with time. Phenomena that are observed in this Letter are novel and realizable in practical devices such as coupled waveguides where the refractive index is a function of time. © 2019 Optical Society of America

Optics Letters

Asymmetric propagation and limited wavelength translation of optical pulses through a linear dispersive time-dynamic system

Exploiting scattering matrix (S-matrix) formalism, a unique route for manipulating the exceptional points (EPs) has been reported in a trilayer open optical microcavity with non-uniform real refractive index. The boundaries of the intermediate index layer are appropriately tapered. The cavity is partially pumped by a transverse distribution of a balanced gain-loss profile. With the strict restriction of balanced gain-loss, controlling infinitesimally small variation of gain-coefficient with simultaneous tapering parameter an EP has been encountered; which is being encircled in cavity parameter space to study dynamics of the coupled states around the EP in the context of robust selective flip-of-state phenomena with lower-asymmetry in state conversion efficiencies. Such a specialty trilayer microcavity with tunable width is reported for the first time; which turns out to be a specific approach to achieve maximum efficiency in conversion with minimum asymmetry. Considering suitable state-of-the-art techniques, this exclusive proposal may open up a fabrication feasible platform for device level implementation of system control exploiting EPs. © 2019 IOP Publishing Ltd.

Journal of Optics (United Kingdom)

Minimally asymmetric state conversion around exceptional singularities in a specialty optical microcavity

The current world averages of the ratios RD(∗) are about 4σ away from their Standard Model prediction. These measurements indicate towards the violation of lepton flavor universality in b → cl ¯ν decay. The different new physics operators, which can explain the RD(*) measurements, have been identified previously. We show that a simultaneous measurement of the polarization fractions of τ and D* and the angular asymmetries AFB and ALT in B → D*τ ¯ν decay can distinguish all the new physics amplitudes and hence uniquely identify the Lorentz structure of new physics. © Springer Nature Switzerland AG 2019.

Springer Proceedings in Physics

Resolving RD and RD* anomalies

The anomalies in the measurements of observables involving b → sμμ decays, namely RK, RK*, P5′, and Bsϕ, may be addressed by adding lepton-universality-violating new physics contributions to the effective operators O9,O10,O9′,O10′. We analyze all the scenarios where the new physics contributes to a pair of these operators at a time. We perform a global fit to all relevant data in the b → s sector to estimate the corresponding new Wilson coefficients, O9NP,O10NP,O9′,O10′. In the light of the new data on RK, and RK*, presented in Moriond 2019, we find that the scenarios with new physics contributions to the (O9NPO9′) or (O9NPO10′) pair remain the most favored ones. On the other hand, though the competing scenario (O9NPO10NP) remains attractive, its advantage above the SM reduces significantly due to the tension that emerges between the RK and RK* measurements with the new data. The movement of the RK measurement towards unity would also result in the re-emergence of the one-parameter scenario C9NP = − C9′. © 2019, The Author(s).

Journal of High Energy Physics

Continuing search for new physics in b → sμμ decays: two operators at a time

We report the first examples of thiocyanate-based analogues of the cyanide Prussian blue compounds, MIII[Bi(SCN)6], M = Fe, Cr, Sc. These compounds adopt the primitive cubic pcu topology and show strict cation order. Optical absorption measurements show these compounds have band gaps within the visible and near IR region, suggesting that they may be useful for applications where light harvesting is key, such as photocatalysis. We also show that Cr[Bi(SCN)6] can reversibly uptake water into its framework structure pointing towards the possibility of using these frameworks for host/guest chemistry. © 2019 The Royal Society of Chemistry.