Engineering topics
Choudhury, D.
Publications and source records attributed to Choudhury, D..
Orbital configuration in CaTiO 3 films on NdGaO 3
Despite its use as a constituent layer for realization of a polar metal and interfacial conductivity, the microscopic study of electronic structure of CaTiO 3 is still very limited. Here, we epitaxially stabilized CaTiO 3 films on NdGaO 3 (110) substrates in a layer-by-layer way by pulsed laser deposition. The structural and electronic properties of the films were characterized by reflection-high-energy-electron-diffraction, X-ray diffraction, and element-specific resonant X-ray absorption spectroscopy. To reveal the orbital polarization and the crystal field splitting of the titanium 3d state, X-ray linear dichroism was carried out on CaTiO 3 films, demonstrating the orbital configuration of d xz /d yz < d xy < d 3z 2 -r 2 < d x 2 -y 2 . To further explore the origin of this configuration, we performed the first-principles density function theory calculations, which linked the orbital occupation to the on-site energy of Ti 3d orbitals. Finally, these findings can be important for understanding and designing exotic quantum states in heterostructures based on CaTiO 3 .
Structure of Te 80 52 132 : The two-particle and two-hole spectrum of Sn 82 50 132
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Magnetic Interactions at the Nanoscale in Trilayer Titanates
We report on the phase diagram of competing magnetic interactions at the nanoscale in engineered ultrathin trilayer heterostructures of LaTiO3/SrTiO3/YTiO3, in which the interfacial inversion symmetry is explicitly broken. Combined atomic layer resolved scanning transmission electron microscopy with electron energy loss spectroscopy and electrical transport have confirmed the formation of a spatially separated two-dimensional electron liquid and high density two-dimensional localized magnetic moments at the LaTiO3/SrTiO3 and SrTiO3/YTiO3 interfaces, respectively. Resonant soft x-ray linear dichroism spectroscopy has demonstrated the presence of orbital polarization of the conductive LaTiO3/SrTiO3 and localized SrTiO3/YTiO3 electrons. Our results provide a route with prospects for exploring new magnetic interfaces, designing a tunable two-dimensional d-electron Kondo lattice, and potential spin Hall applications.
Engineered Mott ground state in a LaTiO 3+δ /LaNiO 3 heterostructure
In pursuit of creating cuprate-like electronic and orbital structures, artificial heterostructures based on LaNiO 3 have inspired a wealth of exciting experimental and theoretical results. However, to date there is a very limited experimental understanding of the electronic and orbital states emerging from interfacial charge transfer and their connections to the modified band structure at the interface. Towards this goal, we have synthesized a prototypical superlattice composed of a correlated metal LaNiO 3 and a doped Mott insulator LaTiO 3+δ , and investigated its electronic structure by resonant X-ray absorption spectroscopy combined with X-ray photoemission spectroscopy, electrical transport and theory calculations. The heterostructure exhibits interfacial charge transfer from Ti to Ni sites, giving rise to an insulating ground state with orbital polarization and e g orbital band splitting. Here, our findings demonstrate how the control over charge at the interface can be effectively used to create exotic electronic, orbital and spin states.
Anomalous charge and negative-charge-transfer insulating state in cuprate chain compound KCuO 2
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Metallic interface in non-SrTiO{sub 3} based titanate superlattice
We report on the fabrication of all perovskite Mott insulator/band insulator YTiO{sub 3}/CaTiO{sub 3} superlattices by pulsed laser deposition. The combination of in situ reflection high energy electron diffraction, X-ray diffraction, and X-ray reflectivity confirms the high quality of the films grown in a layer-by-layer mode. Electrical transport measurements reveal that a non-SrTiO{sub 3} based two-dimensional electron gas system has formed at the YTiO{sub 3}/CaTiO{sub 3} interface. These studies offer another route in the pursuit of complex oxide two-dimensional electron gas systems, which allows to obtain greater insights into the exotic many-body phenomena at such interfaces.
Experience with turbulence interaction and turbulence-chemistry models at Fluent Inc.
This viewgraph presentation discusses (1) turbulence modeling: challenges in turbulence modeling, desirable attributes of turbulence models, turbulence models in FLUENT, and examples using FLUENT; and (2) combustion modeling: turbulence-chemistry interaction and FLUENT equilibrium model. As of now, three turbulence models are provided: the conventional k-epsilon model, the renormalization group model, and the Reynolds-stress model. The renormalization group k-epsilon model has broadened the range of applicability of two-equation turbulence models. The Reynolds-stress model has proved useful for strongly anisotropic flows such as those encountered in cyclones, swirlers, and combustors. Issues remain, such as near-wall closure, with all classes of models.
A Tripler to 220 GHz Using a Back-to-Back Barrier-N-N+ Varactor Diode
The back-to-back barrier-N-N+ (bbBNN) varactor is a nonlinear device being developed for frequency multiplier applications above 100 GHz. Its symmetrical C-V characteristic, low series resistance and suitability to planarization make it ideal choice for high frequency, low power, odd harmonic generation. In this paper, the performance of a 220 GHz tripler using integrated planar bbBNN devices is presented.
Subharmonic Mixer with Planar Schottky Diodes in a Novel Split-Back at 200 - 240 GHz
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Frequency Tripler with Integrated Back-to-Back Barrier -N-N(sup +) (bbBNN) Varactor Diodes in a Novel Split-Waveguide Block at 220 GHz
A frequency tripler has been developed using an integrated planar back-to-back -n-n(sup +) varactor device in a waveguide mount at 220 GHz.
A Tripler to 220 GHz Using a Back-To-Back Barrier-N-N(sup +) Varactor Diode
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Integrated Back-to-Back Barrier-N-N + Varactor Diode Tripler Using a Split-waveguide Block
The back-to-back barrier-N-N + (bbBNN) varactor is a nonlinear device being developed for frequency multiplier applications above 100 GHz. Its symmetrical C-V characteristic, low series resistance and suitability to planarization make it ideal choice for high frequency, low power, odd harmonic generation. In this paper, development of an integrated planar multiplier device and its performance as a 220 GHz tripler is presented. A new split-waveguide block design has been used to provide the proper embedding impedances to the device. The performance over 200-240 GHz has been measured and the integrated bbBNN device is shown to provide as much as 734 microwatts output power. A flange-to-flange tripling efficiency of 7% has been obtained. This is believed to be the highest conversion efficiency yet reported for all planar tripler at this frequency. The performance is expected to be improved further with minor changes to the device and circuit parameters.
Experimental Evaluation and Theoretical Analysis of Back-to-Back Barrier-N-N(sup +)(bbBNN) Varactor Frequency Multipliers for Millimeter and Submillimeter Wave Applications
This paper describes the performance of planar back-to-back Barrier-N-N(sup +)(bbBNN) devices for millimeter and submillimeter wave multiplier applications.