arXiv subjects

Jayanta Bera

Publications and source records attributed to Jayanta Bera.

17 recordsLinked to original sources

arXiv2026

Collective dynamics of harmonically trapped 1D quantum droplets under linear gravitational-like confinement

We investigate the dynamics of harmonically confined quantum droplets in a binary Bose Einstein condensate within the one dimensional extended Gross Pitaevskii framework, including LHY corrections, under a constant linear (gravitational like) potential. By analyzing the COM and width dynamics, we show that the monopole (breathing) mode remains governed by the harmonic confinement, with a frequency asymptotically insensitive to the linear perturbation, demonstrating the robustness of internal collective excitations against uniform external forcing. In contrast, the COM exhibits interaction-dependent transport, with weak confinement producing large susceptibility and rapid displacement, whereas strong confinement suppresses transport even under large forcing. The COM response decreases monotonically with increasing trap frequency. We further characterize the evolving quantum state through the quantum Fisher information and Wigner quasi-probability distributions, showing that the linear potential enables controlled generation of states with enhanced metrological sensitivity over finite times, while stronger confinement shifts the onset of the high-sensitivity regime to larger forcing strengths. Numerical simulations based on the split-step Fourier method confirm the dynamical stability of the obtained solutions. These results illustrate the impact of linear gravitational like trap on the collective excitations, transport, and quantum metrological properties of 1D ultradilute quantum fluids.

cond-mat.quant-gas↗

arXiv2026

Structural Properties and Applications of the Augmented Sombor Index

Topological indices are key quantitative descriptors in mathematical chemistry, unchanged under symmetry operations and retaining graph connectivity; they capture molecular structural features to provide insights into molecular stability and chemical properties, becoming indispensable in cheminformatics and theoretical chemistry. Among degree-based indices, the \textbf{Sombor index} is widely concerned for capturing structural information, and motivated by enhanced structural discrimination, the \textbf{augmented Sombor index} ($ASO$) is defined for a connected graph $\Omega$ with $|V(\Omega)|\geq 3$ as $$ASO(\Omega) = \sum_{v_iv_j\in E(\Omega)} \sqrt{\frac{{d_i^2 + d_j^2}}{d_i + d_j - 2}},$$ where $d_i$ and $d_j$ are the degrees of vertices $v_i$ and $v_j$, respectively. Within the scope of this study, we first establish several sharp bounds for the augmented Sombor index and characterize the extremal graphs attaining these bounds. In particular, we determine the minimum value of the $ASO$ index for unicyclic graphs with a prescribed girth and characterize all graphs achieving this minimum. We also identify the second maximum $ASO$ value among trees and characterize the corresponding extremal tree structures. Furthermore, the minimum and maximum values of the $ASO$ index for bipartite graphs and chemical graphs are obtained, together with a complete characterization of the associated extremal graphs. In addition, we characterize the chemical trees that maximize the $ASO$ index. The chemical applicability of the $ASO$ index is investigated through quantitative structure-property relationship (QSPR) analysis, supported by a comparative assessment of several variants of the Sombor index. Finally, we present concluding remarks and outline potential directions for future research on the augmented Sombor index of graphs.

math.CO↗

arXiv2026

Resolving Open Problems on the Hyper-Zagreb Index and its Chemical Applications

Topological indices are numerical invariants derived from molecular graphs and play an important role in characterizing chemical compounds and predicting their properties. Among the earliest descriptors are the classical Zagreb indices introduced by Gutman and Trinajsti\'c in 1972. A more recent development is the hyper-Zagreb index ($HM$), defined as $HM(G)=\sum_{v_i v_j\in E(G)}(d_i+d_j)^2$, where $d_i$ denotes the degree of vertex $v_i$. In 2023, Hayat et al. posed an open problem concerning bounds on the $HM$ index under fixed vertex-connectivity or edge-connectivity, along with the characterization of the corresponding extremal graphs. In this work, the problem is resolved by determining the extremal graphs that maximize $HM$ index under these constraints. The investigation is further extended to several additional extremal problems, including graphs with a given number of leaves, chromatic number, and independence number. The associated extremal graphs are identified in each case. In addition, the chemical relevance of $HM$ is examined through QSPR studies. Finally, the conclusion is presented.

physics.chem-ph↗

arXiv2025

One-dimensional quantum droplets under linear gravitational-like trap

We investigate the influence of a constant and time-dependent linear gravitational-like potential on one-dimensional quantum droplets (QDs), governed by an extended GPE incorporating a repulsive cubic effective mean-field (EMF) term and an attractive quadratic beyond-mean-field (BMF) correction. Within a tailored external confinement, we analytically characterize the QDs wavefunction and derive the effective interaction contributions. Analogous to classical Newtonian dynamics, the falling velocity of the droplet within a finite domain is found to depend solely on the strength of the linear gravitational like potential, remaining independent of both the total atom number and the magnitude of EMF nonlinearity. When the linear potential is temporally modulated, deviations in the trajectory of the droplet emerge relative to the static case, indicating potential applicability in precision gravimetry. To further probe the dynamical coherence properties, we compute the Shannon entropy and the Wigner quasi-probability distribution. Both measures reveal distinct signatures of the constant and time varying linear potential, with the modulation strength directly influencing the phase-space localization and coherence structure of the droplet. Numerical simulations substantiate the stability of the analytical solutions, demonstrating their robustness. These findings suggest promising implications for quantum sensing and metrological applications using ultradilute quantum fluids.

quant-ph↗

arXiv2025

Resolving Open Problems on the Euler Sombor Index

Recently, the Euler Sombor index $(EUS)$ was introduced as a novel degree-based topological index. For a graph $G$, the Euler Sombor index is defined as $$EUS(G) = \sum_{v_i v_j \in E(G)} \sqrt{d_i^2 + d_j^2 + d_i d_j},$$ where $d_i$ and $d_j$ denote the degrees of the vertices $v_i$ and $v_j$, respectively. Very recently, Khanra and Das \textbf{\bf [Euler Sombor index of trees, unicyclic and chemical graphs, \emph{MATCH Commun. Math. Comput. Chem.} \textbf{94} (2025) 525--548]} proposed several open problems concerning the Euler Sombor index. This paper completely resolves two of the most challenging problems posed therein. First, we determine the minimum value of the $EUS$ index among all unicyclic graphs of a fixed order and prescribed girth, and we characterize the extremal graphs that attain this minimum. Building on this result, we further establish the minimum $EUS$ index within the broader class of connected graphs of the same order and girth, and identify the corresponding extremal structures. In addition, we classify all connected graphs that attain the maximum Euler Sombor index $(EUS)$ when both the order and the number of leaves are fixed.

math.CO↗

arXiv2025

Oscillation-Induced Frequency Generation in 1D Quantum Droplets under Harmonic-Gaussian Confinements

We explore the dynamical behavior of one-dimensional quantum droplets (QDs) governed by the extended Gross-Pitaevskii equation, under harmonic confinement supplemented by a static or time-dependent Gaussian spike (Gs) potential. Employing both variational analytical techniques and numerical simulations, we investigate the evolution of the root-mean-square (RMS) size, excitation spectrum, and phase-space dynamics of QDs. Our study reveals that while the harmonic trap sets the primary confinement, the Gs potential enables precise frequency tuning and control over droplet oscillations. A static Gs amplitude modifies the fundamental oscillation frequency depending on its sign, while a time-modulated Gs induces nonlinear dynamics, including higher harmonics and frequency mixing. Our analysis reveals that the resulting frequency spectrum is strongly influenced by inter- and intra-species interactions as well as by the parameters of the external trap. Notably, we establish a relationship between the frequency shift and the amplitude of the Gaussian spike. Wigner phase-space analysis further uncovers coherent rotational behavior, offering insights into hidden phase dynamics not apparent in real-space density profiles.

cond-mat.quant-gas↗

arXiv2025

Temperature Measurement via Time Crystal Frequencies in One-Dimensional Quantum Droplets

We propose a method for temperature measurement by analyzing the frequency of generated time crystals in one-dimensional (1D) quantum droplets. The system consists of a binary Bose-Einstein condensate mixture confined in a driven quasi-periodic optical lattice (QOL) with repulsive cubic effective mean-field and attractive quadratic beyond-mean-field interactions. By solving the 1D extended Gross-Pitaevskii equation, we derive the exact analytical wavefunction and investigate the droplet dynamics under different driving conditions. Specifically, we examine three cases: (i) constant driving frequency with linearly increasing QOL depth, (ii) constant QOL depth with linearly varying driving frequency, and (iii) constant driving frequency with sinusoidally modulated QOL depth. Fast Fourier Transform analysis reveals harmonic density oscillations, confirming time crystal formation. Additionally, we establish a non-trivial correlation between time crystal frequency and system temperature, demonstrating that an increase in time crystal frequency leads to oscillatory variations in the magnitude of the droplet's negative temperature. Finally, numerical stability analysis confirms that the obtained solutions remain robust, ensuring their feasibility for experimental realization.

cond-mat.quant-gas↗

arXiv2024

Dispersion Managed Elliptical Atomtronics for Interferometry

Circular atomtronics is known to exhibit a uniform ground state, unlike elliptical atomtronics. In elliptical atomtronics, the matter wave tends to accumulate along the semimajor edges during its time dynamics, which we depict by the survival function. Consequently, the dynamical time scales become coupled to the eccentricity, making the dynamics nontrivial for applications. We report that an appropriate dispersion management can decouple the time scales from the eccentricity. One can choose the suitable dispersion coefficient from the overlap function involving the corresponding ground state. We focus on producing distinct fractional matter waves inside an elliptical waveguide to achieve efficient atom interferometry. The said dispersion engineering can recover fractional revivals in the elliptical waveguide, analogous to the circular case. We demonstrate atom interferometry for the engineered elliptical atomtronics, where matter wave interference is mediated by an external harmonic trap for controlled interference patterns.

quant-ph↗

arXiv2022

Excellent thermoelectric performance and impressive optoelectronic properties of Janus monolayer of ZrXY(X=O, S) (Y=S, Se)

Lower-dimensional TMDC materials are suitable for thermoelectric applications for their specific quantum confinement and being distinct in the density of states (DOS). Here we investigated thermoelectric parameters of the 2D TMDC monolayer of ZrXY ((X=O, S,) (Y=S, Se)) by using Density Functional Theory (DFT) combined with Boltzmann Transport Equation (BTE)

physics.comp-ph↗

arXiv2022

A First-principles study on ABBr3 (A = Cs, Rb, K, Na; B = Ge, Sn) halide perovskites for photovoltaic applications

In recent years, halide perovskite-based solar cells have received intensive attention, and demonstrated power conversion efficiency as high as 25.8%. With regard to the toxicity of Pb and the instability of organic elements, all inorganic lead-free perovskites (ILPs) have been extensively studied to achieve comparable or greater photovoltaic performance. In order to develop ILPs as an alternative for solar cell applications, we performed first-principles calculations of ABBr3 perovskites (A = Cs, Rb, K, and Na, and B = Sn, and Ge). Structural, electronic, and optical properties were systematically studied to probe the potentiality in photovoltaic applications. All these ILPs exhibited a direct bandgap in the range of 1.10 to 1.97 eV, highly beneficial for absorbing solar energy. Furthermore, these ILPs demonstrated significant optical absorption (over 105 cm-1) in the whole UV-Vis spectrum. These results will be helpful for designing highly efficient lead-free perovskite solar cells.

cond-mat.mtrl-sci↗

arXiv2021

Low Thermal Conductivity and Interface Thermal Conductance in SnS2

After the discovery of graphene, there have been tremendous efforts in exploring various layered two-dimensional (2D) materials for their potential applications in electronics, optoelectronics, as well as energy conversion and storage. One of such 2D materials, SnS2, which is earth abundant, low in toxicity, and cost effective, has been reported to show a high on/off current ratio, fast photodetection, and high optical absorption, thus making this material promising for device applications. Further, a few recent theoretical reports predict high electrical conductivity and Seebeck coefficient in its bulk counterparts. However, the thermal properties of SnS2 have not yet been properly explored, which are important to materialize many of its potential applications. Here, we report the thermal properties of SnS2 measured using the optothermal method and supported by density functional theory (DFT) calculations. Our experiments suggest very low in-plane lattice thermal conductivity (\k{appa} = 3.20 +- 0.57 W m-1 K-1) and cross-plane interfacial thermal conductance per unit area (g = 0.53 +- 0.09 MW m-2 K-1) for monolayer SnS2 supported on a SiO2/Si substrate. The thermal properties show a dependence on the thickness of the SnS2 flake. Based on the findings of our DFT calculations, the very low value of the lattice thermal conductivity can be attributed to low group velocity, a shorter lifetime of the phonons, and strong anharmonicity in the crystal. Materials with low thermal conductivity are important for thermoelectric applications as the thermoelectric power coefficient goes inversely with the thermal conductivity.

cond-mat.mtrl-sci↗

arXiv2021

Phonon Coupled Scattering Caused Ultralow Lattice Thermal Conductivity and Its Role in The Remarkable Thermoelectric Performance of Newly Predicted SiS2 and SiSe2 monolayers

For high efficiency thermoelectric power conversion not only improvement of materials properties but also prediction and synthesis of new thermoelectric materials is needed. Here we have carried out a systematic investigation on thermoelectric performance of newly predicted two dimensional (2D) semiconducting SiS2 and SiSe2 monolayers of group IVA-VIA family using density functional theory (DFT) and Boltzmann transport equation (BTE). Our computed values of lattice thermal conductivity (kph) are ultralow which result very high thermoelectric figure of merit (ZT) value of 0.78 (0.80) at 500K in SiS2 (SiSe2) monolayer. The ultralow values of kph are attributed to phonon-phonon coupling of acoustic and low frequency optical branches which leads to larger scattering, low group velocity, smaller mean free path and shorter lifetime of phonons. It is also found from our investigation that p-type doping is more effective than n-type doping to get optimal power factor (PF) and ZT. Our theoretical investigation suggests that newly predicted semiconducting SiS2 and SiSe2 monolayers can be very promising thermoelectric materials for fabrication of high efficiency thermoelectric power generator to convert wastage heat into electricity.

cond-mat.mtrl-sci↗

arXiv2021

Matter-wave Fractional Revivals in a Ring Waveguide

We report fractional revival phenomena in an ultracold matter wave inside a ring waveguide. The specific fractional revival times are precisely identified and corresponding spatial density patterns are depicted. Thorough analyses of the autocorrelation function and quantum carpet provide clear evidence of their occurrence. The exhibited theoretical model is in exact conformity of our numerical results. We also investigate the stability of the condensate and a variation of revival time with the diameter of the ring.

physics.atom-ph↗

arXiv2020

Excellent Thermoelectric and Piezoelectric Properties of Differently Stacked Layers of Two-Dimensional Transition Metal Dinitride HfN2

Two-dimensional (2D) transition metal dinitride (HfN2) has been studied for their optoelectronic, piezoelectric, and thermoelectric properties. Both monolayer and bilayer of HfN2 were studied using density functional theory (DFT) and Boltzmann transport equation (BTE). The bilayer of HfN2 with different stacking layers (AA and AB) showed different electronic properties. The optical property of the material suggests that it is a very good absorber in the ultraviolet (UV) region thus, can be used as a UV-photodetector and as an absorber layer in photovoltaic devices. The piezoelectric properties of the material also showed promising behavior as the piezoelectric stress and strain tensors have highest value of 8.97*(10)^(-10) C/m and 12.59 pm/V respectively for the bilayer. The piezoelectric tensors have highest value for AB stacked bilayer. The ZT value of 0.8 at 900 K is also highest for bilayer AB stacked HfN2. These high values of piezoelectric and thermoelectric parameters of the material suggest that the material would be an excellent choice as thermoelectric energy harvesting devices as well as mechanical stress sensor or actuator.

cond-mat.mtrl-sci↗

arXiv2020

Impressive optoelectronic and thermoelectric properties of two-dimensional XI$_2$ (X=Sn, Si): a first principle study

Two-dimensional (2D) metal halides have received more attention because of their electronic and optoelectronic properties. Recently, researchers are interested to investigate the thermoelectric properties of metal halide monolayers because of their ultralow lattice conductivity, high Seebeck coefficient and figure of merit. Here, we have investigated thermoelectric and optoelectronic properties of XI$_2$ (X=Sn and Si) monolayers with the help of density functional theory and Boltzmann transport equation. The structural parameters have been optimized with relaxation of atomic positions. Excellent thermoelectric and optical properties have been obtained for both SnI$_2$ and SiI$_2$ monolayers. For SnI$_2$ an indirect bandgap of 2.06 eV was observed and the absorption peak was found at 4.68 eV. For this the highest ZT value of 0.84 for p-type doping at 600K has been calculated. Similarly, for SiI$_2$ a comparatively low indirect bandgap of 1.63 eV was observed, and the absorption peak was obtained at 4.86 eV. The calculated ZT product for SiI$_2$ was 0.87 at 600K. Both the crystals having high absorbance and ZT value suggest that they can be promising candidates for optoelectronic and thermoelectric devices.

cond-mat.mtrl-sci↗

arXiv2020

Ultralow lattice thermal conductivity and high thermoelectric performance near room temperature of Janus monolayer HfSSe

Two-dimensional transition metal di-chalcogenides (TMDCs) have shown great potential as good quality thermoelectric materials at high temperature since past few years due to their suitable band gap tunabilty, low dimensionality and fantastic combination of electrical conductivity and lattice thermal conductivity. Here, a first principles calculations of electronic and thermoelectric performance of two dimensional monolayer HfS 2 , HfSe 2 and their Janus monolayer HfSSe has been performed with the help of density functional theory and Boltzmann transport equation. Thermodynamical stability of all three structures has been confirmed from phonon dispersion curves. The thermoelectric parameters such as Seebeck coefficient, power factor and electrical conductivity have been calculated at 300K, 400K and 500K. The lattice thermal conductivity at room temperature has been found very low in monolayer HfS 2 , HfSe 2 and HfSSe Janus monolayer as compared to very popular TMDCs such as MoS 2 and WS 2 . An ultralow value of lattice thermal conductivity of the value of 0.36 W/mK at room temperature in Janus monolayer HfSSe has been found which is lower than that of monolayer HfS 2 and HfSe 2 because of the very low group velocity and short phonon lifetime in HfSSe. This ultralow lattice thermal conductivity in Janus monolayer HfSSe results a very high thermoelectric figure of merit close to the value of 1 at room temperature. By constructing the Janus monolayer of HfS 2 and HfSe 2 the thermoelectric performances significantly enhanced. Our theoretical investigation predicts that Janus monolayer HfSSe can be a revolutionary candidate for the fabrication of next generation wearable thermoelectric power generator to convert human body heat into electricity.

cond-mat.mtrl-sci↗

arXiv2019

Strain Induced Enhancement of Thermoelectric Properties of Monolayer WS2 through Valley Degeneracy

Two-dimensional transition metal dichalcogenides show great potential as promising thermoelectric materials due to their lower dimensionality, the unique density of states and quantum confinement of carriers. The effect of mechanical strain on the thermoelectric performances of monolayer WS 2 has been investigated using density functional theory associated with semiclassical Boltzmann transport theory. The variation of Seebeck coefficient and band gap with applied strain has followed the same type of trend. For n-type material the relaxation time scaled power factor(S 2 σ/τ) increases by the application of compressive strain whereas for p- type material it increases with the application of tensile strain. A 77% increase in the power factor has been observed for the n-type material by the application of uniaxial compressive strain. A decrease in lattice thermal conductivity with the increase in temperature causes an almost 40% increase in ZT product under applied uniaxial compressive strain. From the study, it is observed that uniaxial compressive strain is more effective among all types of strain to enhance the thermoelectric performance of monolayer WS 2 . Such strain induced enhancement of thermoelectric properties in monolayer WS 2 could open a new window for the fabrication of high-quality thermoelectric devices.

physics.comp-ph↗