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Fractional revivals are recently reported for circular atomtronics, but get disturbed for a nonzero eccentricity of the waveguide geometry. Here, we provide a mechanism for the elliptical atomtronics with arbitrary eccentricity to restore fractional revivals. The uniform ground state of the circular waveguide becomes nonuniform in the elliptical geometry. An appropriate dispersion management can bring back the uniformity and we use the overlap function numerically to identify the corresponding dispersion coefficients, which match our proposed analytical formula. The fact that the cloud spends mostly along the semimajor edges, is demonstrated by the survival function. The said dispersion management recovers the desired fractional revivals patterns, where the revival time-scale becomes independent of the eccentricity. The present method paves the way also to observe other known phenomena of circular atomtronics in elliptical atomtronics., Comment: 11 pages, 7 figures

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), Comment: 18 page,8 figure

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., Comment: 25 pages, 11 figures, 5 tables

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.

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.

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., Comment: 6 pages, 4 figures

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.

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.

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.

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 {\sigma}/{\tau}) 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.