Showing papers by "Birabar Nanda published in 2021"
TL;DR: In this article, the authors proposed a low strained and energetically favorable mono and bilayer graphene overlayer on anatase TiO2 (001) surface and examined the electronic structure of the interface with the aid of first principle calculations.
11 citations
21 Jun 2021
TL;DR: In this article, the octahedral distortion in halide double perovskites Cs2AgMCl6 through iso-trivalent substitution at the M site was demonstrated.
Abstract: Halide perovskite materials recently attracted wide attention for light-emitting applications. The intense white light emission and excited state lifetimes greater than 1 μs are the hallmarks of a good light-emitting material. Here, we provide a clear design strategy to achieve both of these aforementioned properties in a single material via the introduction of octahedral asymmetry in halide double perovskites Cs2AgMCl6 through iso-trivalent substitution at the M site. In the substituted Cs2AgMCl6, the presence of mixed M3+ sites distorts the [AgCl6]5- octahedra, affecting the parity of the valence and conduction band edges and thereby altering the optical transitions. The distortion also creates a local polarization that leads to an effective photogenerated carrier separation. Considering perovskite series with three M3+ cations, namely Bi3+, In3+ and Sb3+, the mixed trivalent cationic compounds with specific ratios of In3+ and Bi3+ show white light emission with intensity nearly 150 times larger than that of the parent compounds, and are characterised by excited state lifetimes nearing 1 μs. Using single crystal X-ray diffraction, far-infrared absorption, steady-state and time-resolved photoluminescence, bias-dependent photoluminescence, P-E loop traces and density-functional theory calculations, we hence demonstrate the role of octahedral distortion in enhancing white light emission and excited state lifetimes of halide double perovskites. Halide perovskites recently attracted wide attention for light emitting applications. Here, octahedral distortion in halide double perovskites Cs2AgMCl6, induced by the mixture of trivalent M-cations Bi3+, In3+, and Sb3+, gives rise to enhanced white light emissivity and longer photoluminescence lifetimes.
11 citations
23 Aug 2021
7 citations
TL;DR: In this article, the effect of dimensionality on transport properties of d-electron-based heavy-fermion metal CaCu3 Ru4 O12 was investigated and a metal-insulator transition is observed below 3 nm film thickness for which sheet resistance crosses, the quantum resistance in 2D.
Abstract: Artificial confinement of electrons by tailoring the layer thickness has turned out to be a powerful tool to harness control over competing phases in nano-layers of complex oxides. We investigate the effect of dimensionality on transport properties of d -electron–based heavy-fermion metal CaCu3 Ru4 O12 . Transport behavior evolves from metallic to localized regime upon reducing thickness and a metal-insulator transition is observed below 3 nm film thickness for which sheet resistance crosses , the quantum resistance in 2D. Magnetotransport study reveals a strong interplay between inelastic and spin-orbit scattering lengths upon reducing thickness, which results in weak-antilocalization (WAL) to weak-localization (WL) crossover in magnetoconductance.
6 citations
TL;DR: Using first principles electronic structure calculations and MD simulations, this paper examined the adsorption and catalytic conversion of 2,4,6-trinitrotoluene (TNT) on the rutile(r) TiO2 (110) surface.
6 citations
TL;DR: In this article, a local-probe muon spin relaxation (SR) and complementary thermodynamic measurements accompanied by first-principles calculations are performed to demonstrate novel electronic structure and magnetic phases of Ba[Formula: see text]MnTeO, where Mn ions with S = 5/2 spins constitute a perfect triangular lattice.
Abstract: Frustrated magnets based on oxide double perovskites offer a viable ground wherein competing magnetic interactions, macroscopic ground state degeneracy and complex interplay between emergent degrees of freedom can lead to correlated quantum phenomena with exotic excitations highly relevant for potential technological applications. By local-probe muon spin relaxation ([Formula: see text]SR) and complementary thermodynamic measurements accompanied by first-principles calculations, we here demonstrate novel electronic structure and magnetic phases of Ba[Formula: see text]MnTeO[Formula: see text], where Mn[Formula: see text] ions with S = 5/2 spins constitute a perfect triangular lattice. Magnetization results evidence the presence of strong antiferromagnetic interactions between Mn[Formula: see text] spins and a phase transition at [Formula: see text] = 20 K. Below [Formula: see text], the specific heat data show antiferromagnetic magnon excitations with a gap of 1.4 K, which is due to magnetic anisotropy. [Formula: see text]SR reveals the presence of static internal fields in the ordered state and short-range spin correlations high above [Formula: see text]. It further unveils critical slowing-down of spin dynamics at [Formula: see text] and the persistence of spin dynamics even in the magnetically ordered state. Theoretical studies infer that Heisenberg interactions govern the inter- and intra-layer spin-frustration in this compound. Our results establish that the combined effect of a weak third-nearest-neighbour ferromagnetic inter-layer interaction (owing to double-exchange) and intra-layer interactions stabilizes a three-dimensional magnetic ordering in this frustrated magnet.
5 citations
TL;DR: Th thickness dependent MIT in Ga-doped ZnO (Ga:ZnO) thin films grown by pulsed laser deposition technique is reported and it is found that due to surface reconstruction and Ga doping, strong crystalline disorder sets in very thin films to introduce localized states and thereby, restricts the donor electron mobility.
Abstract: Understanding and tuning of metal-insulator transition (MIT) in oxide systems is an interesting and active research topics of condensed matter physics. We report thickness dependent MIT in Ga-doped ZnO (Ga:ZnO) thin films grown by pulsed laser deposition technique. From the electrical transport measurements, we find that while the thinnest film (6 nm) exhibits a resistivity of 0.05 Ω cm, lying in the insulating regime, the thickest (51 nm) has resistivity of 6.6 × 10-4 Ω cm which shows metallic type of conduction. Our analysis reveals that the Mott's variable range hopping model governs the insulating behavior in the 6 nm film whereas the 2D weak localization (WL) phenomena is appropriate to explain the electron transport in the thicker Ga:ZnO films. Magnetoresistance study further confirms the presence of strong localization in 6 nm film while WL is observed in 20 nm and above thicker films. From the density functional calculations, it is found that due to surface reconstruction and Ga doping, strong crystalline disorder sets in very thin films to introduce localized states and thereby, restricts the donor electron mobility.
4 citations
TL;DR: In this paper, the Slater-Koster tight-binding model (SK-TB) was proposed to reproduce the bulk and surface electronic structure in the vicinity of the Fermi level.
Abstract: The halide perovskites have truly emerged as efficient optoelectronic materials and show the promise of exhibiting nontrivial topological phases. Since the bandgap is the deterministic factor for these quantum phases, here we present a comprehensive electronic structure study using first-principle methods by considering nine inorganic halide perovskites CsBX$_3$ (B = Ge, Sn, Pb; X = Cl, Br, I) in their three structural polymorphs (cubic, tetragonal and orthorhombic). A series of exchange-correlations (XC) functionals are examined towards accurate estimation of the bandgap. Furthermore, while thirteen orbitals are active in constructing the valence and conduction band spectrum, here we establish that a four orbital based minimal basis set is sufficient to build the Slater-Koster tight-binding model (SK-TB), which is capable of reproducing the bulk and surface electronic structure in the vicinity of the Fermi level. Therefore, like the Wannier based TB model, the presented SK-TB model can also be considered as an efficient tool to examine the bulk and surface electronic structure of halide family of compounds. As estimated by comparing the model study and DFT band structure, the dominant electron coupling strengths are found to be nearly independent of XC functionals, which further establishes the utility of the SK-TB model.
3 citations
TL;DR: In this article, the Slater-Koster tight-binding (SK-TB) model was proposed to reproduce the bulk and surface electronic structures in the vicinity of the Fermi level.
Abstract: The halide perovskites have truly emerged as efficient optoelectronic materials and show the promise of exhibiting nontrivial topological phases. Since the bandgap is the deterministic factor for these quantum phases, here, we present a comprehensive electronic structure study using first-principle methods by considering nine inorganic halide perovskites CsBX3 (B = Ge, Sn, Pb; X = Cl, Br, I) in their three structural polymorphs (cubic, tetragonal, and orthorhombic). A series of exchange–correlation (XC) functionals are examined toward accurate estimation of the bandgap. Furthermore, while 13 orbitals are active in constructing the valence and conduction band spectra, here, we establish that a 4 orbital based minimal basis set is sufficient to build the Slater–Koster tight-binding (SK-TB) model, which is capable of reproducing the bulk and surface electronic structures in the vicinity of the Fermi level. Therefore, like the Wannier based TB model, the presented SK-TB model can also be considered an efficient tool to examine the bulk and surface electronic structures of the halide family of compounds. As estimated by comparing the model study and DFT band structure, the dominant electron coupling strengths are found to be nearly independent of XC functionals, which further establishes the utility of the SK-TB model.
2 citations
TL;DR: In this article, the symmetry and substitution-driven electronic phase transition in BaPbO$_3$ and BaPnO$O$1-x}$Sn$_x $O$3$ was studied and two end members were found to be insulating.
Abstract: Density functional calculations are carried out to study the symmetry and substitution-driven electronic phase transition in BaPb$_{1-x}$Sn$_x$O$_3$. Two end members BaSnO$_3$ and BaPbO$_3$, are found to be insulating and metallic, respectively. In the latter case, the metallicity arises with the presence of an electron pocket, formed by Pb-s dominated conduction band edge, and a hole pocket formed O-p dominated valence bands. While electron carriers are found to be highly mobile, the hole carriers are localized. Our study reveals that an insulating phase can be realized in the metallic cubic BaPbO$_3$ in three ways in order to explore optoelectronic properties. Firstly, by lowering the symmetry of the lattice to monoclinic through rotation and tilting of the PbO$_6$ octahedra. Secondly, by hydrostatic pressure, and thirdly by alloying with Sn substitution. The presence of soft phonon modes implies the plausibility of symmetry lowering structural transitions. Furthermore, unlike the earlier reports, we find that Sn substituted BaPbO$_3$ cannot exhibits topological insulator phase due to absence of the band inversion.
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TL;DR: In this article, a Hamiltonian using quasi-degenerate perturbation theory was developed to describe polarized field driven band structures and unique topological phases for the universal class of Halide perovskites including both inorganic and hybrid members.
Abstract: Halide perovskites are perceived to be the promising class of materials for optoelectronics, spinorbitronics and topological electronics due to presence of strong spin-orbit coupling and polarized field. Here, we develop a Hamiltonian using quasi-degenerate perturbation theory to describe polarized field driven band structures and unique topological phases such as Dirac semimetallic rings for the universal class of Halide perovskites including both inorganic and hybrid members. The spin textures obtained through this theoretical model captures minute effects of polarization and hence can be used as a modern tool to determine the polarized field directions which have significant influence on spinorbitronics. The analysis brings out the concepts of hybrid spin textures intermixing the effects of valence and conduction bands under topological quantum phase transitions, and spin texture binaries where alignment of the spins are reversed between domains in the momentum space with sharp boundaries. The results are validated through density functional calculations.
TL;DR: In this article, the symmetry and substitution-driven electronic phase transition in BaPb1−xSnxO3 was investigated and the authors showed that an insulating phase can be realized in the metallic cubic BaPpO3 in three ways in order to explore optoelectronic properties: first, by lowering the symmetry of the lattice to monoclinic through rotation and tilting of the PbO6 octahedra; second, by hydrostatic pressure; and third, by alloying with Sn substitution.
Abstract: Density functional calculations are carried out to study the symmetry and substitution-driven electronic phase transition in BaPb1−xSnxO3. Two end members, BaSnO3 and BaPbO3, are found to be insulating and metallic, respectively. In the latter case, the metallicity arises with the presence of an electron pocket, formed by Pb-s dominated conduction band edge, and a hole pocket formed by O-p dominated valence bands. While electron carriers are found to be highly mobile, the hole carriers are localized. Our study reveals that an insulating phase can be realized in the metallic cubic BaPbO3 in three ways in order to explore optoelectronic properties: first, by lowering the symmetry of the lattice to monoclinic through rotation and tilting of the PbO6 octahedra; second, by hydrostatic pressure; and third, by alloying with Sn substitution. The presence of soft phonon modes implies the plausibility of symmetry lowering structural transitions. Furthermore, unlike the earlier reports, we find that Sn substituted BaPbO3 cannot exhibit the topological insulator phase due to the absence of the band inversion.