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Your search keyword '"Ray, Rajyavardhan"' showing total 11 results
Start Over Author "Ray, Rajyavardhan" Topic density functional theory
11 results on '"Ray, Rajyavardhan"'

1. Finite temperature fluctuation-induced order and responses in magnetic topological insulators

Author

Scholten, Marius, Facio, Jorge I., Ray, Rajyavardhan, Eremin, Ilya M., Brink, Jeroen van den, and Nogueira, Flavio S.

Subjects
High Energy Physics - Theory, Condensed Matter - Strongly Correlated Electrons, Strongly Correlated Electrons (cond-mat.str-el), High Energy Physics - Theory (hep-th), Condensed Matter - Mesoscale and Nanoscale Physics, Mesoscale and Nanoscale Physics (cond-mat.mes-hall), FOS: Physical sciences, Condensed Matter::Strongly Correlated Electrons, field theory, magnetic topological insulators, density functional theory, Monte Carlo simulation
Abstract

We derive an effective field theory model for magnetic topological insulators and predict that a magnetic electronic gap persists on the surface for temperatures above the ordering temperature of the bulk. Our analysis also applies to interfaces of heterostructures consisting of a ferromagnetic and a topological insulator. In order to make quantitative predictions for MnBi$_2$Te$_4$, and for EuS-Bi$_2$Se$_3$ heterostructures, we combine the effective field theory method with density functional theory and Monte Carlo simulations. For MnBi$_2$Te$_4$ we predict an upwards N\'eel temperature shift at the surface up to $15 \%$, while the EuS-Bi$_2$Se$_3$ interface exhibits a smaller relative shift. The effective theory also predicts induced Dzyaloshinskii-Moriya interactions and a topological magnetoelectric effect, both of which feature a finite temperature and chemical potential dependence., Comment: v2: published version, LaTeX 15 pages, 5 figures

Published
2021
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2. Bi12Rh3Cu2I5: A 3D Weak Topological Insulator with Monolayer Spacers and Independent Transport Channels.

Author

Carrillo-Aravena, Eduardo, Finzel, Kati, Ray, Rajyavardhan, Richter, Manuel, Heider, Tristan, Cojocariu, Iulia, Baranowski, Daniel, Feyer, Vitaliy, Plucinski, Lukasz, Gruschwitz, Markus, Tegenkamp, Christoph, and Ruck, Michael

Subjects
TOPOLOGICAL insulators, SPIN-orbit interactions, PHOTOELECTRON spectroscopy, QUANTUM computing, DENSITY functional theory, DIRAC function
Abstract

Topological insulators (TIs) are semiconductors with protected electronic surface states that allow dissipation‐free transport. TIs are envisioned as ideal materials for spintronics and quantum computing. In Bi14Rh3I9, the first weak 3D TI, topology presumably arises from stacking of the intermetallic [(Bi4Rh)3I]2+ layers, which are predicted to be 2D TIs and to possess protected edge‐states, separated by topologically trivial [Bi2I8]2− octahedra chains. In the new layered salt Bi12Rh3Cu2I5, the same intermetallic layers are separated by planar, i.e., only one atom thick, [Cu2I4]2− anions. Density functional theory (DFT)‐based calculations show that the compound is a weak 3D TI, characterized by Z2=(0;0001), and that the topological gap is generated by strong spin–orbit coupling (Eg,calc. ∼ 10 meV). According to a bonding analysis, the copper cations prevent strong coupling between the TI layers. The calculated surface spectral function for a finite‐slab geometry shows distinct characteristics for the two terminations of the main crystal faces ⟨001⟩, viz., [(Bi4Rh)3I]2+ and [Cu2I4]2−. Photoelectron spectroscopy data confirm the calculated band structure. In situ four‐point probe measurements indicate a highly anisotropic bulk semiconductor (Eg,exp. = 28 meV) with path‐independent metallic conductivity restricted to the surface as well as temperature‐independent conductivity below 60 K. [ABSTRACT FROM AUTHOR]

Published
2022
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3. Optical And Electronic Properties Of Double Perovskite Ba2ScSbO6.

Author

Ray, Rajyavardhan, Himanshu, A. K., Lahiri, J., Kumar, Uday, Sen, Pintu, Bandyopadhyay, S. K., and Sinha, T. P.

Subjects
*OPTICAL properties of barium compounds, *DENSITY functional theory, *SPACE groups, *PEROVSKITE, *ELECTRONIC structure, *SOLID state chemistry
Abstract

The ordered double perovskite Ba2ScSbO6 (BSS) has been synthesized in polycrystalline form by solid state reaction at 1400 C for 72 Hrs. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Rietveld analysis. The crystal structure is cubic, with space group Fm-3m (No. 225) and lattice parameter, a = 8.20 Å. Optical band-gap has been calculated using UV-Vis Spectroscopy and Kubelka-Munk (KM) function, yielding 4.23 eV. A detailed Abinitio Density Functional Theory (DFT) study of the electronic properties has been carried out using the Full-Potential Linear Augmented Plane Wave (FP-LAPW) as implemented in WIEN2k. BSS is found to be a large band-gap insulator with potential technological applications. [ABSTRACT FROM AUTHOR]

Published
2016
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4. Optical And Electronic Properties Of Double Perovskite Ba2ScSbO6.

Author

Ray, Rajyavardhan, Himanshu, A. K., Lahiri, J., Kumar, Uday, Sen, Pintu, Bandyopadhyay, S. K., and Sinha, T. P.

Subjects
OPTICAL properties of barium compounds, DENSITY functional theory, SPACE groups, PEROVSKITE, ELECTRONIC structure, SOLID state chemistry
Abstract

The ordered double perovskite Ba2ScSbO6 (BSS) has been synthesized in polycrystalline form by solid state reaction at 1400 C for 72 Hrs. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Rietveld analysis. The crystal structure is cubic, with space group Fm-3m (No. 225) and lattice parameter, a = 8.20 Å. Optical band-gap has been calculated using UV-Vis Spectroscopy and Kubelka-Munk (KM) function, yielding 4.23 eV. A detailed Abinitio Density Functional Theory (DFT) study of the electronic properties has been carried out using the Full-Potential Linear Augmented Plane Wave (FP-LAPW) as implemented in WIEN2k. BSS is found to be a large band-gap insulator with potential technological applications. [ABSTRACT FROM AUTHOR]

Published
2016
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5. Phase Transitions In Double Perovskite Sr2ScSbO6: An Ab-initio Study.

Author

Ray, Rajyavardhan, Himanshu, Ajay K., Brajesh, Kumar, Bandyopadhyay, S. K., Kumar, Uday, and Sinha, T. P.

Subjects
*PHASE transitions, *PEROVSKITE, *STRONTIUM compounds, *AB initio quantum chemistry methods, *DENSITY functional theory, *ELECTRONIC structure, *BAND gaps
Abstract

First Principles study of the electronic properties of recently synthesized double perovskite Sr2ScSbO6 have been performed using density functional theory. With increasing temperature, the Sr compound undergoes three structural phase transitions at 400K, 550K and 650K approximately, leading to the following sequence of phases: P21/n → I2/m → I4/m → Fm-3m. Starting from the monoclinic phase P21/n at room temperature, resulting from the Sc/Sb ordering, the electronic structure for the tetragonal I4/m at 613K and cubic Fm-3m for T≤ 660K has been studied in terms of the density of states and band-structure. Presence of large band gap, both direct and indirect, has been reported and analyzed. [ABSTRACT FROM AUTHOR]

Published
2014
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6. Electronic Structure of Ordered Double Perovskite Ba2CoWO6.

Author

Ray, Rajyavardhan, Himanshu, A. K., Brajesh, Kumar, Choudhary, B. K., Bandyopadhyay, S. K., Sen, Pintu, Kumar, Uday, and Sinha, T. P.

Subjects
*ELECTRONIC structure, *PEROVSKITE, *BARIUM compounds, *POLYCRYSTALS, *CHEMICAL synthesis, *SOLID state chemistry, *X-ray diffraction
Abstract

Ba2CoWO6 (BCoW) has been synthesized in polycrystalline form by solid state reaction at 1200 °C. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Rietveld analysis of the XRD pattern. The crystal structure is cubic, space group Fm-3m (No. 225) with the lattice parameter, a = 8.210. Optical bandgap of the present system has been calculated using the UV-Vis Spectroscopy and Kubelka-Munk function, it's value being 2.45 eV. A detailed study of the electronic properties has also been carried out using the density functional theory (DFT) techniques implemented on WIEN2k. Importance of electron-electron interaction between the Co ions leading to half-metallic behavior, crystal and exchange splitting together with the hybridization between O and Co, W has been investigated using the total and partial density of states. [ABSTRACT FROM AUTHOR]

Published
2014
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7. Electronic Structure of Ordered Double Perovskite Ba2CoWO6.

Author

Ray, Rajyavardhan, Himanshu, A. K., Brajesh, Kumar, Choudhary, B. K., Bandyopadhyay, S. K., Sen, Pintu, Kumar, Uday, and Sinha, T. P.

Subjects
ELECTRONIC structure, PEROVSKITE, BARIUM compounds, POLYCRYSTALS, CHEMICAL synthesis, SOLID state chemistry, X-ray diffraction
Abstract

Ba2CoWO6 (BCoW) has been synthesized in polycrystalline form by solid state reaction at 1200 °C. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Rietveld analysis of the XRD pattern. The crystal structure is cubic, space group Fm-3m (No. 225) with the lattice parameter, a = 8.210. Optical bandgap of the present system has been calculated using the UV-Vis Spectroscopy and Kubelka-Munk function, it's value being 2.45 eV. A detailed study of the electronic properties has also been carried out using the density functional theory (DFT) techniques implemented on WIEN2k. Importance of electron-electron interaction between the Co ions leading to half-metallic behavior, crystal and exchange splitting together with the hybridization between O and Co, W has been investigated using the total and partial density of states. [ABSTRACT FROM AUTHOR]

Published
2014
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8. Electronic structure calculation of Sr2CoWO6 double perovskite using DFT+U.

Author

Mandal, Golak, Jha, Dhiraj, Himanshu, A. K., Ray, Rajyavardhan, Mukherjee, P., Das, Nisith, Singh, B. K., Sreenivas, K., Singh, M. N., Sinha, A. K., Singh, Biswas, and Das

Subjects
SYNCHROTRONS, RAMAN spectroscopy, LATTICE constants, DENSITY functional theory, ELECTRIC insulators & insulation, SEMIMETALS, BAND gaps
Abstract

Using the synchrotron and Raman spectroscopy we measured the lattice parameter and Raman modes of the half-metallic (HM) Sr2CoWO6 (SCoW) synthesied by the solid state reaction technique.. The physical properties of SCoW are studies within the framework of density function theory (DFT) under the generalised gradient approximation (GGA) of Perdew, Bruke, and Ernzerhof both by itself and including a coulomb repulsion via the Hubbard approach or GGA+U. Our results states that Sr2CoWO6 material behaves as insulators for the spin-up orientation and spindown orientation as found for the half metallic systems and at U = 0.06eV the ground state of spin up channel being insulating with spin gap of 2.27eV comparable to the experimental Band gap (BG). [ABSTRACT FROM AUTHOR]

Published
2018
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9. Ab-initio study of double perovskite Ba2YSbO6.

Author

Mondal, Golak, Jha, D., Himanshu, A. K., Lahiri, J., Singh, B. K., Kumar, Uday, Ray, Rajyavardhan, Singh, Biswas, and Das

Subjects
DENSITY functional theory, ELECTRONIC structure, PEROVSKITE, POLYCRYSTALS, X-ray diffraction, LATTICE constants, PLANE wavefronts
Abstract

The density functional theory with generalized gradient approximation has been used to investigate the electronic structure of double perovskite oxide Ba2YSbO6 (BYS) synthesized in polycrystalline form by solid state reaction. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Riedvelt analysis of the XRD pattern. The crystal structure is cubic, space group being Fm-3m (No. 225) with the lattice parameter, a = 8.424 Ǻ. Optical band-gap of this system has been calculated using UV-Vis Spectroscopy and Kubelka-Munk (KM) function, having the value 4.56eV. A detailed study of the electronic properties has also been carried out using the Full-Potential Linear Augmented Plane Wave (FPLAPW) as implemented in WIEN2k. BYS is found to be a large band-gap insulator with potential technological applications, such as dielectric resonators and filters in microwave applications. [ABSTRACT FROM AUTHOR]

Published
2018
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10. Multiple low-energy excitons and optical response of [formula omitted] double perovskite Ba[formula omitted]ScTaO[formula omitted].

Author

Himanshu, A.K., Kumar, Sujit, Dey, Urmimala, and Ray, Rajyavardhan

Subjects
*EXCITON theory, *DENSITY functional theory, *PEROVSKITE, *DIELECTRIC resonators, *REFLECTANCE measurement
Abstract

Large bandgap insulators are considered promising for applications such as photocatalysts, dielectric resonators and interference filters. Based on synchrotron X-ray diffraction, diffuse reflectance measurement and density functional theory, we report the crystal structure, optical response, and electronic properties of the synthesized d 0 double perovskite Ba 2 ScTaO 6. In contrast to earlier prediction, the electronic bandgap is found to be large, ∼ 4. 66 eV. The optical response is characterized by the presence of multiple exciton modes extending up to the visible range. A detailed investigation of the direct gap excitons based on the Elliot formula is presented. Density functional theory based investigation of the electronic properties within generalized gradient approximation severely underestimates the electronic gap. To reach a quantitative agreement, we consider different available flavors of the modified-Becke–Johnson exchange–correlation potential and discuss their effects on the electronic and optical properties. • Experimental characterization based on Synchrotron X-ray diffraction (SXRD) and determination of electronic optical gap via UV–Vis spectroscopy. • Identification of multiple exciton modes with large binding energies, extending up to the visible range of the electromagnetic spectrum. • Test of different flavors of mBJ potential within density functional theory (DFT) as Ba2 ScTaO6 , although perovskite oxide, has a large gap. • Detailed investigation of electronic structure and optical response in terms of multiple low-energy exciton modes. [ABSTRACT FROM AUTHOR]

Published
2022
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11. Ab-initio study of double perovskite Ba2YSbO6.

Author

Mondal, Golak, Jha, D., Himanshu, A. K., Lahiri, J., Singh, B. K., Kumar, Uday, Ray, Rajyavardhan, Singh, Biswas, and Das

Subjects
*DENSITY functional theory, *ELECTRONIC structure, *PEROVSKITE, *POLYCRYSTALS, *X-ray diffraction, *LATTICE constants, *PLANE wavefronts
Abstract

The density functional theory with generalized gradient approximation has been used to investigate the electronic structure of double perovskite oxide Ba2YSbO6 (BYS) synthesized in polycrystalline form by solid state reaction. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Riedvelt analysis of the XRD pattern. The crystal structure is cubic, space group being Fm-3m (No. 225) with the lattice parameter, a = 8.424 Ǻ. Optical band-gap of this system has been calculated using UV-Vis Spectroscopy and Kubelka-Munk (KM) function, having the value 4.56eV. A detailed study of the electronic properties has also been carried out using the Full-Potential Linear Augmented Plane Wave (FPLAPW) as implemented in WIEN2k. BYS is found to be a large band-gap insulator with potential technological applications, such as dielectric resonators and filters in microwave applications. [ABSTRACT FROM AUTHOR]

Published
2018
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