Solid State Physics Laboratory

About: Solid State Physics Laboratory is a facility organization based out in Delhi, India. It is known for research contribution in the topics: Quantum dot & Dielectric. The organization has 1754 authors who have published 2597 publications receiving 50601 citations.

Effect ofA-site andB-site substitution on the infrared reflectivity spectra ofLa1−yAyMn1−xBxO3(A=Ba,Sr;B=Cu,Zn,Sc;0<y<~0.3;0<~x<~0.1)manganites

Abstract: We have measured the infrared reflectivity spectra of ${\mathrm{La}}_{1\ensuremath{-}y}[\mathrm{Sr}(\mathrm{Ba}){]}_{y}{\mathrm{Mn}}_{1\ensuremath{-}x}[\mathrm{Cu}(\mathrm{Zn},\mathrm{Sc}){]}_{x}{\mathrm{O}}_{3}$ $(0lyl~0.3,0l~xl~0.10)$ manganites, in a wide frequency $(100\char21{}4000{\mathrm{cm}}^{\ensuremath{-}1})$ and temperature (80 K\char21{}300 K) range. The reflectivity spectra were analyzed by a fitting procedure based on a model that includes Drude, midinfrared electronic, and phonon oscillator contributions to the dielectric constant. Six infrared active ${(3A}_{u}$ and ${3E}_{u})$ modes of rhombohedral symmetry are clearly observed. We assigned all observed modes according to existing lattice dynamical calculations for the rhombohedral structure of ${\mathrm{LaMnO}}_{3}.$ A decrease of the rhombohedral distortion below the paramagnetic-ferromagnetic transition is manifested through a lowering or complete removal of the frequency difference between the ${A}_{u}$ and ${E}_{u}$ modes.

Role of AlGaN/GaN interface traps on negative threshold voltage shift in AlGaN/GaN HEMT

Abstract: This article reports negative shift in the threshold-voltage in AlGaN/GaN high electron mobility transistor (HEMT) with application of reverse gate bias stress. The device is biased in strong pinch-off and low drain to source voltage condition for a fixed time duration (reverse gate bias stress), followed by measurement of transfer characteristics. Negative threshold voltage shift after application of reverse gate bias stress indicates the presence of more carriers in channel as compared to the unstressed condition. We propose the presence of AlGaN/GaN interface states to be the reason of negative threshold voltage shift, and developed a process to electrically characterize AlGaN/GaN interface states. We verified the results with Technology Computer Aided Design (TCAD) ATLAS simulation and got a good match with experimental measurements.

Raman mapping of a single-layer to double-layer graphene transition

Abstract: We report on confocal Raman spectroscopy on a few-layer graphene flake. Adjacent single- and double-layer graphene sections allow mapping the transition in vibrational and electronic properties to a second stacked graphene sheet and with it a weak interlayer coupling. Most prominently the width of the D' peak doubles upon going from a single to a double layer, which can be explained within the double-resonant Raman model. The intensities of the G and G' lines decrease at the crossover to a single layer. Contrary to the G' line the G peak position shifts to higher wave numbers, however, not uniformly over the entire section: its frequency fluctuates spatially. The Raman map of the D line intensity shows a non-zero contribution at the boundaries of the flake and the individual sections, which can be attributed either to defects and disorder or to the breakdown of translational symmetry, whereas within the flake no D line signal is detected.

Scanning gate microscopy measurements on a superconducting single-electron transistor

Abstract: We present measurements on a superconducting single-electron transistor (SET) in which the metallic tip of a low-temperature scanning force microscope is used as a movable gate. We characterize the SET through charge stability diagram measurements and compare them to scanning gate measurements taken in the normal conducting and the superconducting states. The tip-induced potential is found to have a rather complex shape. It consists of a gate voltage-dependent part and a part which is independent of gate voltage. Further scanning gate measurements reveal a dependence of the charging energy and the superconducting gap on the tip position and the voltage applied to it. We observe an unexpected correlation between the magnitude of the superconducting gap and the charging energy. The change in EC can be understood to be due to screening, however the origin of the observed variation in Δ remains to be understood. Simulations of the electrostatic problem are in reasonable agreement with the measured capacitances.