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S. Mukhopadhyay

Publications and source records attributed to S. Mukhopadhyay.

At least 19 recordsLinked to original sources

Physics-informed interpretable forms for dipole resonances and quantities relevant for astrophysics

We have employed Bayesian inference to extract the centroid energies and widths from the isovector giant dipole resonance (IVGDR) data for the IVGDR built on the ground states of nuclei.These IVGDR properties were modeled by explicitly incorporating the structural effects like isospin asymmetry, nuclear deformation and shell correction. The resulting parametrizations reproduce the IVGDR systematics with remarkable precision for both spherical and axially deformed nuclei. Subsequently, the extracted IVGDR parameters were used to constrain the coefficients of the nuclear symmetry energy, which are found to be in good agreement with recent measurements of nuclear dipole polarizability. Furthermore, these symmetry-energy coefficients were employed to predict the dipole polarizability within different self-consistent mean-field models and to investigate its correlation with the neutron-skin thickness. The present findings provide valuable input for large-scale calculations of radiative capture processes relevant to nuclear astrophysics and for improving our understanding of astrophysical scenarios under extreme conditions.

nucl-th↗

The effect of duty cycle on electron transmission through a graphene electrostatic barrier

We investigated theoretically the transmission properties of Dirac Fermions tunneling through a periodically (sinusoidal and rectangular) driven electrostatic barrier in Monolayer graphene. For the time harmonic potential with moderate to high alpha (=amplitude/frequency) the central Floquet band is found to be almost cloaked for the Klein transmitted electron in contrast to electron at higher grazing incidences. As a time periodic drive, we mainly focused on the use of rectangular wave electric signal to modulate the transparency of the barrier. It is noted that the asymmetric Fano resonance, a characteristic feature of photon assisted tunneling, is more likely to occur for rectangular drive in contrast to the harmonic one. The height of the modulating potential is particularly responsible for the dressing effect of the barrier. The position and nature of the FR can be tailored by changing the height and frequency of the rectangular drive. Moreover, the duty cycle of the driving potential turns out to be an important controlling parameter for the transmission process. Thus, the rectangular modulation plays an important role for the occurrence and detection of the Fano resonances which is vital for the use of graphene nanostructure in the field of detectors, sensors, modulators etc. The present findings attempt for the first time, to realize the effect of duty cycle on the quantum interference in semiconductor nanostructures.

cond-mat.mes-hall↗

Measurement of the Hoyle State Radiative Transition Width

The radiative decay of the Hoyle state is the doorway to the production of heavier elements in stellar environment. Here we report, an exclusive measurement of electric quadruple (E$_2$) transitions of the Hoyle state to the ground state of $^{12}$C through the $^{12}$C(p, p$^\prime$$γ$$γ$)$^{12}$C reaction. Triple coincidence measurement yields a value of radiative branching ratio $Γ_{rad}$/$Γ$ = 4.01 (30) $\times$ 10$^{-4}$. The result has been corroborated by an independent experiment based on the complete kinematical measurement $via.$ $^{12}$C(p, p$^\prime$)$^{12}$C reaction ($Γ_{rad}$/$Γ$ = 4.04 (30) $\times$ 10$^{-4}$). Using our results together with the currently adopted values of $Γ_π$(E$_0$)/$Γ$ and $Γ_π$($E_0$), the radiative width of the Hoyle state is found to be 3.75 (40) $\times$ 10$^{-3}$ eV. We emphasize here that our result is not in agreement with 34 $\%$ increase in the radiative decay width of the Hoyle state measured recently but consistent with the currently adopted value.

nucl-ex↗

High-harmonic generation from subwavelength silicon films

Recent years have witnessed significant developments in the study of nonlinear properties of various optical materials at the nanoscale. However, in most cases experimental results on harmonic generation from nanostructured materials are reported without the benefit of suitable theoretical models and appropriate comparisons to assess enhancement of conversion efficiencies compared to the intrinsic properties of a given material. Here, we report experimental observations of even and odd optical harmonics generated from a suspended subwavelength silicon film, a dielectric membrane, up to the 7th harmonic tuned deep in the UV range at 210nm, which is the current limit of our detection system, using peak power densities of order 3TW/cm^2. We explain the experimental data with a time domain, hydrodynamic-Maxwell approach broadly applicable to most materials. Our approach accounts simultaneously for surface and magnetic nonlinearities that generate even optical harmonics, as well as linear and nonlinear material dispersions beyond the third order to account for odd optical harmonics, plasma formation, and a phase locking mechanism that makes the generation of high harmonics possible deep into the UV range, where semiconductors like silicon start operating in a metallic regime.

physics.optics↗

Dual relaxation oscillations in a Josephson junction array

We report relaxation oscillations in a one-dimensional array of Josephson junctions. The oscillations are circuit-dual to those ordinarily observed in single junctions. The dual circuit quantitatively accounts for temporal dynamics of the array, including the dependence on biasing conditions. Injection locking the oscillations results in well-developed current plateaux. A thermal model explains the relaxation step of the oscillations.

cond-mat.mes-hall↗

Below the Surface: Unraveling the Intricacies of the Nonlinear Optical Properties of Aluminum through Bound Electrons

By uncovering novel aspects of second harmonic generation in aluminum we show that there are unusual and remarkable consequences of resonant absorption, namely an unexpectedly critical role that bound electrons play for light-matter interactions across the optical spectrum, suggesting that a different basic approach is required to fully explain the physics of surfaces. We tackle an issue that is never under consideration given the generic hostile conditions to the propagation of light under resonant absorption. Unlike most noble metals, aluminum displays Lorentz-like behavior and interband transitions centered near 810 nm, thus splitting the plasmonic range in an atypical manner and setting its linear and nonlinear optical properties apart. Studies of aluminum nanostructures having complex topologies abound, as do reported inconsistencies in the linear spectral response of surface plasmons and harmonic generation. Our experimental observations of second harmonic generation from aluminum nanolayers show that bound electrons are responsible for a unique signature neither predicted nor observed previously: a hole in the second harmonic spectrum. A hydrodynamic-Maxwell theory explains these findings exceptionally well and becomes the basis for renewed studies of surface physics.

physics.optics↗

Search for the origin of wobbling motion in the $ A \approx 130 $ region: The case of $^{131}$Xe

In-beam $ γ$-ray spectroscopy of $^{131}$Xe has been carried out to study the structure of the intruder $ νh_{11/2} $ band. Excited states were populated via an $ α$-induced fusion-evaporation reaction at E$ _α = 38 $ MeV. Inspection of $ γγ$-coincidence data resulted in the identification of a new rotational sequence. Based on the systematics of excitation energy, assigned spin-parity, decay pattern, and the electromagnetic character of the inter-band $ ΔI = 1 $ $ γ$-transitions, this sequence is proposed as the unfavoured signature partner of the $ νh_{11/2} $ band. The structure of this band is further illuminated in the light of the triaxial particle rotor model (TPRM). The possibility of wobbling excitation in $ N = 77 $ Xe-Ba-Ce isotones has been explored in a systematic manner.

nucl-ex↗

Precise determination of quadrupole and hexadecapole deformation parameters of the $sd$-shell nucleus, $^{28}$Si

Quasi-elastic (QEL) scattering measurements have been performed using $^{28}$Si projectile off a $^{90}$Zr target at energies around the Coulomb barrier. A Bayesian analysis within the framework of coupled channels (CC) calculations is performed in a large parameter space of quadrupole and hexadecapole deformations ($β_{2}$ and $β_{4}$) of $^{28}$Si. Our results clearly show that $^{28}$Si is an oblate shaped nucleus with $β_{2}$=-$0.38 \pm 0.01$ which is in excellent agreement with electromagnetic probes. A precise value of hexadecapole deformation for $^{28}$Si, $β_{4}$=+$0.03 \pm 0.01$, along with a consistent value of quadrupole deformation has now been determined for the first time using QEL scattering. A remarkable agreement between the experimental $β_{4}$ value of $^{28}$Si and Skyrme-Hartree-Fock based calculations is obtained. The QEL results obtained previously for $^{24}$Mg (prolate) and the present result for $^{28}$Si (oblate) hereby affirm the strong sensitivity of the quasi-elastic scattering to ground state deformations, thus reinforcing its suitability as a potential probe for rare exotic nuclei.

nucl-ex↗

Dramatic enhancement of second and third harmonic generation in gold nanogratings in the visible and UV ranges

Notwithstanding its long history, the study of nonlinear optics from metal surfaces is still an active field of research. For instance, in view of the presence of absorption questions remain concerning the possibility of significantly enhancing harmonic conversion efficiencies in the visible and UV ranges. While to many it may seem that metals do not easily lend themselves to that purpose, they are nevertheless crucial materials in the development of nanophotonics, and more generally, to electromagnetism at the nanoscale. Here, we report our experimental observations and numerical simulations of second and third harmonic generation from a gold nanograting, which exhibits a plasmonic resonance whose spectral position depends on incident angle. All things being equal, the enhancement of nonlinear optical processes from the UV to the near IR range manifests itself in dramatic manner: second harmonic generation conversion efficiencies increase more than three orders of magnitude compared to a flat gold mirror, while third harmonic generation conversion efficiency increases by nearly four orders of magnitude, both in excellent agreement with predictions. The clear inferences one may draw from our results are that our model describes the dynamics with unprecedented accuracy, and that much remains to be revealed in the development of nonlinear optics of metals at the nanoscale.

physics.optics↗

Superconductivity from a melted insulator

Quantum phase transitions typically result in a broadened critical or crossover region at nonzero temperature. Josephson arrays are a model of this phenomenon, exhibiting a superconductor-insulator transition at a critical wave impedance, and a well-understood insulating phase. Yet high-impedance arrays used in quantum computing and metrology apparently evade this transition, displaying superconducting behavior deep into the nominally insulating regime. The absence of critical behavior in such devices is not well understood. Here we show that, unlike the typical quantum-critical broadening scenario, in Josephson arrays temperature dramatically shifts the critical region. This shift leads to a regime of superconductivity at high temperature, arising from the melted zero-temperature insulator. Our results quantitatively explain the low-temperature onset of superconductivity in nominally insulating regimes, and the transition to the strongly insulating phase. We further present, to our knowledge, the first understanding of the onset of anomalous-metallic resistance saturation. This work demonstrates a non-trivial interplay between thermal effects and quantum criticality. A practical consequence is that, counterintuitively, the coherence of high-impedance quantum circuits is expected to be stabilized by thermal fluctuations.

cond-mat.mes-hall↗

Optical and electrical properties of Nd3+doped Na2O-ZnO-TeO2 Material

Neodymium doped Na2O-ZnO-TeO2 (NZT) glasses were prepared by the conventional melt quenching technique. DTA and TG were used to confirmation of glass preparation through the glass transition temperature at 447°C for the glass system. The analysis of FTIR spectra and X-ray diffraction described the nature of the samples were ionic and amorphous respectively. The optical bandgap energy was estimated using absorption spectra and found to be decreased from 2.63eV to 1.32 eV due to the increase of doping concentration. The intensity of the emission spectra was enhanced for the higher concentration of Nd3+ ions. The dielectric constant of the glass samples was found to be constant for the large range of frequency (3 kHz to 1 MHz). The variation of conductivity with the temperature of the samples had shown the Arrhenius mechanism of conduction.

cond-mat.mtrl-sci↗

Measurement of relative isotopic yield distribution of even-even fission fragments from $^{235}$U($n_{th}$,$f$) following $γ$ ray spectroscopy

A detailed investigation on the relative isotopic distributions has been carried out for the first time in case of even-even correlated fission fragments for the $^{235}$U($n_{th}$,$f$) fission reaction. High-statistics data were obtained in a prompt $γ$ ray spectroscopy measurement during the EXILL campaign at ILL, Grenoble, France. The extensive off-line analysis of the coincidence data have been carried out using four different coincidence methods. Combining the results from 2-dimensional $γ-γ$ and 3-dimensional $γ-γ-γ$ coincidence analysis, a comprehensive picture of the relative isotopic yield distributions of the even-even neutron-rich fission fragments has emerged. The experimentally observed results have been substantiated by the theoretical calculations based on a novel approach of isospin conservation, and a reasonable agreement has been obtained. The calculations following the semi-empirical GEF model have also been carried out. The results from the GEF model calculations are found to be in fair agreement with the experimental results.

nucl-ex↗

Nuclear level density and thermal properties of $^{115}$Sn from neutron evaporation

The nuclear level density of $^{115}$Sn has been measured in an excitation energy range of $\sim $2 - 9 MeV using the experimental neutron evaporation spectra from the $^{115}$In($p,n$)$^{115}$Sn reaction. The experimental level densities were compared with the microscopic Hartree-Fock BCS (HFBCS), Hartree-Fock-Bogoliubov plus combinatorial (HFB+C), and an exact pairing plus independent particle model (EP+IPM) calculations. It is observed that the EP+IPM provides the most accurate description of the experimental data. The thermal properties (entropy and temperature) of $^{115}$Sn have been investigated from the measured level densities. The experimental temperature profile as well as the calculated heat capacity show distinct signatures of a transition from the strongly-paired nucleonic phase to the weakly paired one in this nucleus.

nucl-ex↗

Evidence for the reduction of nuclear level density away from the $β$-stability line

The isospin dependence of nuclear level density has been investigated by analyzing the spectra of evaporated neutrons from excited $^{116}$Sn and $^{116}$Te nuclei. These nuclei are populated via $p$ + $^{115}$In and $^{4}$He + $^{112}$Sn reactions in the excitation energy range of 18 - 26 MeV. Because of low excitation energy, the neutron spectra are predominantly contributed by the first-chance decay leading to the $β$-stable $^{115}$Sn and neutron-deficient $^{115}$Te as residues for the two cases. Theoretical analysis of the experimental spectra have been performed within the Hauser-Feshbach formalism by employing different models of the level density parameter. It is observed that the data could only be explained by the level density parameter that decreases monotonically when the proton number deviates from the $β$-stable value. This is also confirmed by performing a microscopic shell-model calculation with the Wood-Saxon mean field. The results have strong implication on the estimation of the level density of unstable nuclei, and calculation of astrophysical reaction rates relevant to $r$- and $rp$-processes.

nucl-ex↗

Detailed investigation on the possibility of using EJ-299-33A plastic scintillator for fast neutron spectroscopy in large scale experiments

Detailed characterization of the newly available plastic scintillator (EJ-299-33A) having the pulse shape discrimination (PSD) property has been carried out in case of a large-sized detector (5 in.$\times$5 in.). The pulse height response of the scintillator for nearly mono-energetic neutrons has been reported in case of neutron energies E$_n$ =3, 6 and 9 MeV. Important properties (figure-of-merit (FOM), time resolution, detection efficiency) of the detector has been compared with a commonly used liquid organic scintillator based detector of the same size coupled to the same PMT for uniformity in comparison. The results show that the plastic scintillator detector has about 12$\%$ better time resolution. However, the FOM and detection efficiency were found to be lower than that of the liquid scintillator detector by 40 - 50$\%$ and $\sim $25$\%$, respectively. The possibility of using the new plastic scintillator in large-scale nuclear physics experiments has been pointed out.

physics.ins-det↗

Excitation energy and angular momentum dependence of the nuclear level density parameter around A$\approx $110

Neutron kinetic energy spectra in coincidence with low-energy $γ$-ray multiplicities have been measured around $A\approx $ 110 in the $^{16}$O, $^{20}$Ne + $^{93}$Nb reactions in a compound nuclear excitation energy range of $\approx $ 90 - 140 MeV. The excitation energy (temperature) and angular momentum (spin) dependence of the inverse level density parameter $k$ has been investigated by comparing the experimental data with statistical Hauser-Feshbach calculation. In contrast to the available systematic in this mass region, the inverse level density parameter showed an appreciable increase as a function of the excitation energy. The extracted $k$-values at different angular momentum regions, corresponding to different $γ$-multiplicities also showed an overall increase with the average nuclear spins. The experimental results have been compared with a microscopic statistical-model calculation and found to be in reasonable agreement with the data. The results provide useful information to understand the variation of nuclear level density at high temperature and spins.

nucl-ex↗

$E0$ transition strength in stable Ni isotopes

Excited states in $^{58,60,62}$Ni were populated via inelastic proton scattering at the Australian National University as well as via inelastic neutron scattering at the University of Kentucky Accelerator Laboratory. The Super-e electron spectrometer and the CAESAR Compton-suppressed HPGe array were used in complementary experiments to measure conversion coefficients and $δ(E2/M1)$ mixing ratios, respectively, for a number of $2^+ \rightarrow 2^+$ transitions. The data obtained were combined with lifetimes and branching ratios to determine $E0$, $M1$, and $E2$ transition strengths between $2^+$ states. The $E0$ transition strengths between $0^+$ states were measured using internal conversion electron spectroscopy and compare well to previous results from internal pair formation spectroscopy. The $E0$ transition strengths between the lowest-lying $2^+$ states were found to be consistently large for the isotopes studied.

nucl-ex↗

Ordered magnetism in the intrinsically decorated $j\rm{_{eff}}$ = $\frac{1}{2}$ $α$-CoV$_{3}$O$_{8}$

The antiferromagnetic mixed valence ternary oxide $α$-CoV$_{3}$O$_{8}$ displays disorder on the Co$^{2+}$ site that is inherent to the $Ibam$ space group. The zero field structural and dynamic properties of $α$-CoV$_{3}$O$_{8}$~have been investigated using a combination of neutron and x-ray diffraction, DC susceptibility, and neutron spectroscopy. The low temperature magnetic and structural properties are consistent with a random macroscopic distribution of Co$^{2+}$ over the 16$k$ metal sites. However, by applying the sum rules of neutron scattering we observe the collective magnetic excitations are parameterized with an ordered Co$^{2+}$ arrangement and critical scattering consistent with a three dimensional Ising universality class. The low energy spectrum is well-described by Co$^{2+}$ cations coupled $via$ a three dimensional network composed of competing ferromagnetic and stronger antiferromagnetic superexchange within the $ab$ plane and along $c$, respectively. While the extrapolated Weiss temperature is near zero, the 3D dimensionality results in long range antiferromagnetic order at $T\rm{_{N}}\sim$ 19 K. A crystal field analysis finds two bands of excitations separated in energy at $\hbar ω$ $\sim$ 5 meV and 25 meV, consistent with a $j\rm{_{eff}}=\frac{1}{2}$ ground state with little mixing between spin-orbit split Kramers doublets. A comparison of our results to the random 3D Ising magnets and other compounds where spin-orbit coupling is present indicate that the presence of an orbital degree of freedom, in combination with strong crystal field effects and well-separated $j\rm{_{eff}}$ manifolds may play a key role in making the dynamics largely insensitive to disorder.

cond-mat.str-el↗