Department of Physics
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Item Systematic study of CVD-growth parameters in NaCl-assisted growth of MoSe2 nanostructures: nanoribbons, dendrites and spirals(RSC, 2025-05) Dey, SrijataMoSe2, a two-dimensional (2D) transition metal dichalcogenide (TMDC), has garnered significant interest in recent years due to its semiconducting properties and tunable band gap with potential applications in optoelectronics, photocatalysis and atomically thin devices. In this study, we report the controlled synthesis of MoSe2 nanocrystals using a custom 12-zone atmospheric pressure chemical vapour deposition (APCVD) system. NaCl is used as a seed promoter to facilitate the growth of monolayer, bilayer, and multilayer films, often as large as 200 μm. Additionally, the morphological evolution of the MoSe2 nanostructures is controlled by tuning different growth parameters based on insights, which we discuss in detail. The growth of dominant nanostructures, which include nanoribbons, snowflakes, monolayers and multilayer domains, among others, are discussed. High-resolution optical microscopy, field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) are used to image the as-grown crystals. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) are used to verify the quality and elemental composition of our as-grown MoSe2 crystals. Our findings brighten the prospect of growing novel 1D and 2D TMDC nanostructures with sufficient control to make them suitable for advanced optoelectronic and catalytic devices.Item Search for new resonances decaying to pairs of merged diphotons in proton-proton collisions at √ = 13 tev(APS, 2025-01) Mukherjee, SajalA search is presented for an extended Higgs sector with two new particles, 𝑋 and 𝜙 , in the process 𝑋→𝜙𝜙→(𝛾𝛾)(𝛾𝛾) . Novel neural networks classify events with diphotons that are merged and determine the diphoton masses. The search uses LHC proton-proton collision data at √𝑠=13 TeV collected with the CMS detector, corresponding to an integrated luminosity of 138 fb−1 . No evidence of such resonances is seen. Upper limits are set on the production cross section for 𝑚𝑋 between 300 and 3000 GeV and 𝑚𝜙/𝑚𝑋 between 0.5% and 2.5%, representing the most sensitive search in this channel.Item Observation of W Z γ production and constraints on new physics scenarios in proton-proton collisions at √s = 13 TeV(APS, 2025-07) Mukherjee, SajalA measurement of the 𝑊𝑍𝛾 triboson production cross section is presented. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of √𝑠 =13 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb−1 . The analysis focuses on the final state with three charged leptons, ℓ±𝜈ℓ+ℓ− , where ℓ =𝑒 or 𝜇 , accompanied by an additional photon. The observed (expected) significance of the 𝑊𝑍𝛾 signal is 5.4 (3.8) standard deviations. The cross section is measured in a fiducial region, where events with an ℓ originating from a tau lepton decay are excluded, to be 5.48 ±1.11 fb , which is compatible with the prediction of 3.69 ±0.24 fb at next-to-leading order in quantum chromodynamics. Exclusion limits are set on anomalous quartic gauge couplings and on the production cross sections of massive axionlike particles.Item Search for fractionally charged particles in proton-proton collisions at √s = 13 TeV(APS, 2025-04) Mukherjee, SajalA search is presented for fractionally charged particles with charges below 1𝑒 , using their small energy loss in the tracking detector as a key variable to observe a signal. The analyzed dataset corresponds to an integrated luminosity of 138 fb−1 of proton-proton collisions collected at √𝑠 =13 TeV in 2016–2018 at the CERN LHC. This is the first search at the LHC for new particles with a charge between 𝑒/3 and 0.9𝑒, including an extension of previous results at a charge of 2𝑒/3 . Masses up to 640 GeV and charges as low as 𝑒/3 are excluded at 95% confidence level. These are the most stringent limits to date for the considered Drell-Yan-like production mode.Item Pure gauss–bonnet nut black hole solution: II(Springer, 2025-05) Mukherjee, SajalIn the present article, we have obtained an exact analytical solution of six-dimensional pure Gauss–Bonnet gravity in the presence of both NUT and Maxwell charges. The topology of the horizon is chosen to be the product of two 2-spheres. Upon evaluating the solution, we study the spacetime properties, such as the event horizon and singularity, and obtain the ranges of parameter space where the solution is valid. We discuss how the presence of Maxwell charges may impact the solution’s asymptotic expansion and what distinctive effects it will bring to the geometry. The thermodynamic properties of the solution are also discussed, emphasizing the interplay between NUT and Maxwell charges.Item Search for the rare decay D0 → μ+μ− in proton-proton collisions at s√ = 13.6 TeV(Hai Science, 2025) Mukherjee, SajalA search for the rare decay D0→μ+μ− is reported using proton-proton collision events at s√ = 13.6 TeV collected by the CMS detector in 2022−2023, corresponding to an integrated luminosity of 64.5 fb−1. This is the first analysis to use a newly developed inclusive dimuon trigger, expanding the scope of the CMS flavor physics program. The search uses D0 mesons obtained from D∗+→ D0π+ decays. No significant excess is observed. A limit on the branching fraction of B(D0→μ+μ−) < 2.4 × 10−9 at 95% confidence level is set. This is the most stringent upper limit set on any flavor changing neutral current decay in the charm sector.Item Impact of a third body on binary neutron star tidal interactions(2025-11) Mukherjee, SajalFor waveform modelling of compact binary coalescence, it is conventionally assumed that the binary is in isolation. In this work, we break that assumption and introduce a third body at a distance. The primary goal is to understand how the distant third body would affect the binary dynamics. However, in the present work, we treat the three-body problem perturbatively and study tidal interaction in the binary due to the third body's presence. We introduce appropriate modifications to the equations governing the orbital motions and the evolution equations of the binary component's quadrupole moment. Further, we obtain the radiated energy and accumulated dephasing for the binary. We show that for b-EMRI, the effect is weak in the tidal sector, while for systems such as b-IMRIs, it would be most relevant to study these effects.Item The curious case of parabolic encounters: gravitational waves with linear & non-linear memory(2025-11) Mukherjee, SajalThe memory effect is known to introduce a permanent displacement in the gravitational wave (GW) detectors after the passage of a GW signal. While the linear memory adheres to the source properties, the non-linear memory is a secondary effect sourced by the GW itself. In the present work, we discuss GW signals with both these kinds of memory effects, while focusing on the parabolic limit of an encounter. This special case is theoretically intriguing and emerges as a limiting situation for both eccentric and hyperbolic events. However, in this paper, we argue that a simple extrapolation of memory calculations for eccentric or hyperbolic cases to the parabolic case may lead to incorrect estimations. Therefore, we treat the parabola as a special case and use an intrinsic parameterization, with which we calculate gravitational wave signals and their energy spectrum via an effective field theory formalism. Unlike the hyperbolic case, which is known to have linear memory, we notice that parabolic encounters bring out new features in the zero frequency limit (ZFL). Our work highlights some of the key challenges and salient aspects of these encounters, and paves the way to study such binary evolution with nonzero memory.Item Thin film of porphyrin for heavy metal ion sensing(Wiley, 2025-05) Gupta, Raj KumarThin film science and technology is one of the important fields of research and development. The reduction in the dimension of bulk material by approaching a limit of 2-dimensional (2D) system through the fabrication of ultrathin films of the material provides a remarkable increase in surface-to-volume (S-V) ratio as compared to its bulk form. Such an enhancement in surface-to-volume ratio increases the activities of material enormously and thereby material properties like catalysis, reactivity, and adhesion are enhanced remarkably. This research study deals with the development of ultrathin film of 5,10,15,20-tetraphenylporphyrin molecule-based sensor which is capable of addressing the problem of water pollution caused by heavy toxic metal ions such as cadmium, cobalt, lead, and mercury. In sensing applications, in addition to the physicochemical properties of the molecules, the nature of aggregation governs the sensing performance. Under the controlled environment of a laboratory, the ultrathin film of tetraphenylporphyrin deposited on a transducer surface with different assemblies of molecules and their sensing performance are highlighted in this chapterItem Active and passive electrode matrix optimization technique to improve humidity sensing performance of MoS2-based devices: unfolding an innovative avenue(IEEE, 2025-05) Gupta, Raj KumarActive electrodes” that are primarily used for the collection of carriers and “passive electrodes” that actively take part in target gas molecule dissociation (gas-induced carrier generation but not collection), owing to their catalytic nature, were judiciously coupled and optimized in a matrix for the first time with an aim to enhance humidity sensing performance of the MoS2-based devices. Intrigued by the design concept of electroencephalogram (EEG) electrode configurations, the present endeavor uniquely adapted the electrode matrix for gas-sensing scenarios. MoS2 nanoflowers were synthesized through hydrothermal deposition, while Pd electrodes, which were used both as active and passive ones, were deposited by electron beam evaporation using a suitably designed metal shadow mask. The innovation of this study lies in the strategic incorporation of catalytic Pd-based electrodes (both as active and passive), where two active electrodes ( 2×2 mm) facilitated signal transmission to the measurement unit, while multiple passive electrodes ( 0.5×0.5 mm) enabled carrier generation through catalytic dissociation of the target gas. The optimum number of passive electrodes was identified to be six offering the highest response magnitude (RM). The optimized sensor was tested across a relative humidity (RH) range of 8%–84%, demonstrating an RM of 54.4% at 84% RH. To provide deeper insight into the sensing mechanism, a theoretical model was developed to quantitatively correlate the RM with RH levels. Comparison with the existing resistive humidity sensors demonstrated the superior performance of the developed sensor, making it a strong candidate for applications in industrial humidity control, healthcare, smart IoT systems, and environmental monitoring.