D.C. Jain

Study of anomalous temperature dependence of itinerant holes in under- and overdoped La2-xSrxCuO4 single crystals using polarised soft X-ray absorption spectroscopy

Abstract Some experiments have recently shown that in the YBCO detwinned system charge aggregation takes place in the Cu–O2 plane along the b-axis at T≫Tc followed by formation of Cooper pairs, again in the normal state. Polarised X-ray absorption measurements at the O K and Cu L3 absorption edges in E∥b orientation have been carried out on underdoped and overdoped single crystals of La2−xSrxCuO4 through a temperature range of 10–300 K to study the dependence of the itinerant hole density. Both the crystals do show an anomalous temperature dependence but there is a wide divergence in the earlier and our results. This paper discusses the results and possible causes for the difference.

Comparative study of the electronic structure of natural and synthetic rubies using XAFS and EDAX analyses

We have studied the Cr-K-edge XANES and EXAFS in natural Indian rubies from two sources and a synthetic ruby at ESRF. Weight % of various constituents in them is determined using EDAX measurements. Taking the results from the three techniques together we are able to demonstrate their feasibility in quantitative study of precious stones.

XANES study of intermediate valence in SmSe1-x Asx alloys

X-ray absorption near edge structure (XANES) measurements on LII edge of Sm are employed to study the intermediate valence in SmSe1-x Asx (0.0 ≤ x ≤ 1.0) solid solutions in which the substitution of trivalent anion As for Se2− drives Sm to a higher valence from divalent towards trivalent in the SmSe lattice. Two absorption peaks corresponding to two different valent states of Sm provide direct evidence for mixed valence of Sm in these alloys. The split white line at the LII edge of Sm is used to determine the Sm mean valence in the alloys. Average valence data deduced from Sm LII edge XANES shows a continuous valence transition with increasing As concentration upto 80 at.% of As. At 90 at.% of As the Sm is fully converted into trivalent state. Mean valence data for Sm shows fair agreement with those measured employing other techniques.

Photoluminescence and atomic force microscopy studies on pre- and post-irradiated ruby with Fe3+ ion

Photoluminescence spectra measured for pristine ruby and its two irradiated samples with Fe3+ ion show R1, R2, N lines and a broad band. Decrease in intensities of these features is observed with irradiation of Fe3+ ion in ruby. Progressive structural changes and modifications on surface of irradiated rubies with Fe3+ ion have been observed by atomic force microscopy. Decrease in intensities is discussed in terms of pair formation.

XANES AND ATOMIC FORCE MICROSCOPY STUDIES ON PRE- AND POST-IRRADIATED SAPPHIRE

XANES measurements at the Fe-K edge on natural South African sapphire single crystal (corundum) and an irradiated sample with fluence 1 × 1012Ni6+ions/cm2 are reported. Some decrease in intensity of pre-edge features (1s → 3d) and increase in intensity of 1s → 4p transition in Fe is observed with Ni fluence. Structural changes and modification on surface of irradiated sapphire with Ni6+ ion have been observed by the atomic force microscopy technique and discussed in the term of defects.

XANES Study of Copper Valence and Structure in High Tc Superconducting Oxides

The question of Cu3+ and role it may play in the mechanism of the HTSC in the perovskites recently has been examined in depth employing XPS and XANES techniques [1–5]. The Cu 2p XPS and valence band emission from CuO and YBa2 Cu3O7-x when discussed along with the CuL3, XANES in these clearly ruled out the presence of Cu3+ and established that the holes are instead situated in the oxygen band. This is further reinforced by the presence of additional peak in the O ls XPS emission. Measurements and one-electron full-multiple scattering calculations on the CuK XANES establish that the best fits to experimental data are obtained employing the 3d10 configuration for copper [6]. The question of alternative structure proposed by Reller, Bednorz and Muller is also examined and rejected through these calculations.