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Sitangshu Bhattacharya

Bio: Sitangshu Bhattacharya is an academic researcher from Indian Institutes of Information Technology. The author has contributed to research in topics: Electron & Magnetic field. The author has an hindex of 13, co-authored 127 publications receiving 570 citations. Previous affiliations of Sitangshu Bhattacharya include St. Xavier's College-Autonomous, Mumbai & Indian Institute of Information Technology, Allahabad.


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05 Dec 2008
TL;DR: The Einstein relation in Compound Semiconductors under Magnetic Quantization (QP) was studied in this paper, where it was shown that the Einstein relation can be found in Inversion Layers and Nipi structures of compound semiconductors in the presence of external fields.
Abstract: Basics of the Einstein Relation- The Einstein Relation in Bulk Specimens of Compound Semiconductors- The Einstein Relation in Compound Semiconductors Under Magnetic Quantization- The Einstein Relation in Compound Semiconductors Under Crossed Fields Configuration- The Einstein Relation in Compound Semiconductors Under Size Quantization- The Einstein Relation in Quantum Wires of Compound Semiconductors- The Einstein Relation in Inversion Layers of Compound Semiconductors- The Einstein Relation in Nipi Structures of Compound Semiconductors- The Einstein Relation in Superlattices of Compound Semiconductors in the Presence of External Fields- The Einstein Relation in Compound Semiconductors in the Presence of Light Waves- The Einstein Relation in Compound Semiconductors Under Magnetic Quantization- Conclusion and Future Research

30 citations

Journal ArticleDOI
TL;DR: In this article, a fully ab initio methodology was used to demonstrate how lattice vibrations couple with neutral excitons in monolayer and contribute to the nonradiative excitonic lifetime.
Abstract: Using a fully ab initio methodology, we demonstrate how the lattice vibrations couple with neutral excitons in monolayer ${\mathrm{WSe}}_{2}$ and contribute to the nonradiative excitonic lifetime. We show that only by treating the electron-electron and electron-phonon interactions at the same time is it possible to obtain an unprecedented agreement of the zero- and finite-temperature optical gaps and absorption spectra with the experimental results. The bare energies were calculated by solving the Kohn-Sham equations, whereas ${G}_{0}{W}_{0}$ many-body perturbation theory was used to extract the excited-state energies. A coupled electron-hole Bethe-Salpeter equation was solved incorporating the polaronic energies to show that it is the in-plane torsional acoustic phonon branch that contributes mostly to the $A$ and $B$ exciton buildup. We find that the three $A$, $B$, and $C$ excitonic peaks exhibit different behavior with temperature, displaying different nonradiative linewidths. There is no considerable transition in the strength of the excitons with temperature, but the $A$ exciton remains dark in comparison with the $C$ exciton. Further, all the excitonic peaks redshift as temperature rises. Renormalization of the bare electronic energies by phonon interactions and anharmonic lattice thermal expansion causes a decreasing band gap with increasing temperature. The zero-point energy renormalization (31 meV) is found to be entirely due to the polaronic interaction with a negligible contribution from lattice anharmonicities. These results may have a profound impact on electronic and optoelectronic device technologies based on these monolayers.

26 citations

Journal ArticleDOI
TL;DR: In this article, a simple theoretical analysis of the effective electron mass (EEM) at the Fermi level for III-V, ternary and quaternary materials, on the basis of a newly formulated electron energy spectra in the presence of light waves whose unperturbed energy band structures are defined by the three-band model of Kane, is presented.
Abstract: We present a simple theoretical analysis of the effective electron mass (EEM) at the Fermi level for III–V, ternary and quaternary materials, on the basis of a newly formulated electron energy spectra in the presence of light waves whose unperturbed energy band structures are defined by the three-band model of Kane The solution of the Boltzmann transport equation on the basis of this newly formulated electron dispersion law will introduce new physical ideas and experimental findings under different external conditions It has been observed that the unperturbed isotropic energy spectrum in the presence of light changes into an anisotropic dispersion relation with the energy-dependent mass anisotropy In the presence of light, the conduction band moves vertically upward and the band gap increases with the intensity and colours of light It has been found, taking n-InAs, n-InSb, n-Hg1−xCdxTe and n-In1−xGaxAsyP1−y lattice matched to InP as examples, that the EEM increases with increasing electron concentration, intensity and wavelength in various manners The strong dependence of the effective momentum mass (EMM) at the Fermi level on both the light intensity and wavelength reflects the direct signature of the light waves which is in contrast with the corresponding bulk specimens of the said materials in the absence of photo-excitation The rate of change is totally band-structure-dependent and is influenced by the presence of the different energy band constants The well known result for the EEM at the Fermi level for degenerate wide gap materials in the absence of light waves has been obtained as a special case of the present analysis under certain limiting conditions, and this compatibility is the indirect test of our generalized formalism

23 citations

Journal ArticleDOI
TL;DR: In this paper, the thermoelectric power in the presence of a large magnetic field (TPM) in heavily doped III-V, II-VI, PbTe/PbSnTe, strained layer and HgTe/CdTe quantum dot superlattices (QDSLs) with graded structures was analyzed.
Abstract: We study theoretically the thermoelectric power in the presence of a large magnetic field (TPM) in heavily doped III–V, II–VI, PbTe/PbSnTe, strained layer and HgTe/CdTe quantum dot superlattices (QDSLs) with graded structures on the basis of newly formulated electron energy spectra and compare the same with that of the constituent materials. It has been found, taking heavily doped GaAs/Ga1−xAlxAs, CdS/CdTe, PbTe/PbSnTe, InAs/GaSb and HgTe/CdTe QDSLs as examples, that the TPM increases with increasing inverse electron concentration and film thickness, respectively, in different oscillatory manners and the nature of oscillations is totally band structure dependent. We have also suggested the experimental methods of determining the Einstein relation for the diffusivity–mobility ratio, the Debye screening length and the electronic contribution to the elastic constants for materials having arbitrary dispersion laws.

23 citations


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23 Apr 2012-Small
TL;DR: Progress in the research and development of carbon nanomaterials during the past twenty years or so for advanced energy conversion and storage is reviewed, along with some discussions on challenges and perspectives in this exciting field.
Abstract: It is estimated that the world will need to double its energy supply by 2050. Nanotechnology has opened up new frontiers in materials science and engineering to meet this challenge by creating new materials, particularly carbon nanomaterials, for efficient energy conversion and storage. Comparing to conventional energy materials, carbon nanomaterials possess unique size-/surface-dependent (e.g., morphological, electrical, optical, and mechanical) properties useful for enhancing the energy-conversion and storage performances. During the past 25 years or so, therefore, considerable efforts have been made to utilize the unique properties of carbon nanomaterials, including fullerenes, carbon nanotubes, and graphene, as energy materials, and tremendous progress has been achieved in developing high-performance energy conversion (e.g., solar cells and fuel cells) and storage (e.g., supercapacitors and batteries) devices. This article reviews progress in the research and development of carbon nanomaterials during the past twenty years or so for advanced energy conversion and storage, along with some discussions on challenges and perspectives in this exciting field.

1,287 citations

Journal ArticleDOI
TL;DR: In this paper, a detailed review of heat conduction research on both individual carbon nanotubes and nanostructured films consisting of arrays or disordered nanotube mats is presented.
Abstract: The extremely high thermal conductivities of carbon nanotubes have motivated a wealth of research. Progress includes innovative conduction metrology based on microfabricated platforms and scanning thermal probes as well as simulations exploring phonon dispersion and scattering using both transport theory and molecular dynamics. This article highlights these advancements as part of a detailed review of heat conduction research on both individual carbon nanotubes and nanostructured films consisting of arrays of nanotubes or disordered nanotube mats. Nanotube length, diameter, and chirality strongly influence the thermal conductivities of individual nanotubes and the transition from primarily diffusive to ballistic heat transport with decreasing temperature. A key experimental challenge, for both individual nanotubes and aligned films, is the separation of intrinsic and contact resistances. Molecular dynamics simulations have studied the impacts of specific types of imperfections on the nanotube conductance and its variation with length and chirality. While the properties of aligned films fall short of predictions based on individual nanotube data, improvements in surface engagement and postfabrication nanotube quality are promising for a variety of applications including mechanically compliant thermal contacts.

379 citations

Journal ArticleDOI
TL;DR: In this article, an ultrathin epitaxial graphite graphite (NPEG) was grown by thermal decomposition on the (0001) surface of 6H-SiC and characterized by surface-science techniques.
Abstract: We have produced ultrathin epitaxial graphite films which show remarkable 2D electron gas (2DEG) behavior. The films, composed of typically 3 graphene sheets, were grown by thermal decomposition on the (0001) surface of 6H-SiC, and characterized by surface-science techniques. The low-temperature conductance spans a range of localization regimes according to the structural state (square resistance 1.5 kOhm to 225 kOhm at 4 K, with positive magnetoconductance). Low resistance samples show characteristics of weak-localization in two dimensions, from which we estimate elastic and inelastic mean free paths. At low field, the Hall resistance is linear up to 4.5 T, which is well-explained by n-type carriers of density 10^{12} cm^{-2} per graphene sheet. The most highly-ordered sample exhibits Shubnikov - de Haas oscillations which correspond to nonlinearities observed in the Hall resistance, indicating a potential new quantum Hall system. We show that the high-mobility films can be patterned via conventional lithographic techniques, and we demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nano-patterned epitaxial graphene (NPEG), with the potential for large-scale integration.

290 citations

Journal ArticleDOI
TL;DR: A review on the status of research in the field of skutterudites can be found in this paper, where an improvement of their efficiencies, stabilities, contacts, industrial scalable fabrication processes and other factors are expected in the near future in order to develop viable modules for intermediate temperature range applications.
Abstract: The research on skutterudites in the last few years has contributed to a better understanding of the physical processes which play an important role in enhancing their thermoelectric performance and to the discovery of novel filled compounds, with one of the most promising zT values at intermediate temperatures. Skutterudites are still an ongoing field of research, and an improvement of their efficiencies, stabilities, contacts, industrial scalable fabrication processes and other factors are expected in the near future in order to develop viable modules for intermediate temperature range applications, such as in the automobile industry, factories or incinerators. This paper gives a review on the status of research in the field of skutterudites.

272 citations