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.

Raman study on single-walled carbon nanotubes with different laser excitation energies

Abstract: The industrial use of carbon nanotubes is increasing day by day; therefore, it is very important to identify the nature of carbon nanotubes in a bundle. In this study, we have used the Raman spectroscopic analysis on vertically aligned single-walled carbon nanotubes (SWCNTs) grown by the chemical vapour deposition (CVD) technique. The grown sample is excited with two laser excitation wavelengths, 633 nm from He-Ne laser and 514·5 nm from Ar+ laser. Raman spectrum in the backscattering geometry provides the characteristic spectra of SWCNTs with its radial breathing mode (RBM), defect-induced disorder mode (D band), and high-energy modes (G and M bands). The Raman signal positions of the spectra in RBM, G and M bands confirm the grown sample to be of semiconducting type in nature.

Low temperature ellipsometry of NaV2O5

Abstract: The dielectric function of ${\ensuremath{\alpha}}^{\ensuremath{'}}$-${\mathrm{NaV}}_{2}{\mathrm{O}}_{5}$ was measured with electric field along the a and b axes in the photon- energy range 0.8--4.5 eV for temperatures down to 4 K. We observe a pronounced decrease of the intensity of the 1-eV peak upon increasing temperature with an activation energy of about 25 meV, indicating that a finite fraction of the rungs becomes occupied with two electrons while others are emptied as temperature increases. No appreciable shifts of peaks were found showing that the change in the valence state of individual V atoms at the phase transition is very small. A remarkable inflection of this temperature dependence at the phase transition at 34 K indicates that charge ordering is associated with the low-temperature phase.

Effects of proton irradiation and ageing on the superconducting properties of single crystalline and polycrystalline MgB2

Abstract: We present magnetization data on crystalline and polycrystalline MgB2 before and after irradiation with ~1 MeV protons. In the virgin crystal the critical current density is below our noise floor of 103 A cm−2 over most of the field range. However, after irradiation a peak occurs in the current density as a function of applied magnetic field as the upper critical field Hc2 is approached. After subsequent ageing over a time period of three months, the peak effect is greatly enhanced, exhibiting much stronger pinning over a wide field range, and the upper critical field is approximately doubled, accompanied by a 2 K reduction in transition temperature. Similar studies were made on polycrystalline fragments, where irradiation leads to an increased irreversibility field (Jc is enhanced at high fields but decreased at low fields) and a suppression in transition temperature. However, after two years of ageing both parameters returned towards those of the virgin sample.