Spectral functions in doped transition metal oxides

We present experimental photoemission and inverse photoemission spectra of SrTiO$_{3- \delta}$ representing electron doped $d^0$ systems. Photoemission spectra in presence of electron doping exhibit prominent features arising from electron correlation effects, while the inverse photoemssion spectra are dominated by spectral features explainable within single-particle approaches. We show that such a spectral evolution in chemically doped correlated systems is not compatible with expectations based on Hubbard or any other similar model. We present a new theoretical approach taking into account the inhomogeneity of the `real' system which gives qualitatively different results compared to standard `homogeneous' models and is in quantitative agreement with experiments.Comment: 10 pages; 1 tex file+4 postscript files (to appear in Europhysics Letters

Estimates of electronic interaction parameters for LaMMO3_3 compounds (MM=Ti-Ni) from ab-initio approaches

We have analyzed the ab-initio local density approximation band structure calculations for the family of perovskite oxides, La$M$O$_3$ with $M$=Ti-Ni within a parametrized nearest neighbor tight-binding model and extracted various interaction strengths. We study the systematics in these interaction parameters across the transition metal series and discuss the relevance of these in a many-body description of these oxides. The results obtained here compare well with estimates of these parameters obtained via analysis of electron spectroscopic results in conjunction with the Anderson impurity model. The dependence of the hopping interaction strength, t, is found to be approximately $r^{-3}$.Comment: 18 pages; 1 tex file+9 postscript files (appeared in Phys Rev B Oct 15,1996

Auger transition from orbitally degenerate systems: Effects of screening and multielectron excitations

We calculate Auger spectra given by the two-hole Green's function from orbitally degenerate Hubbard-like models as a function of correlation strength and band filling. The resulting spectra are qualitatively different from those obtained from fully-filled singly degenerate models due to the presence of screening dynamics and multielectron excitations. Application to a real system shows remarkable agreement with experimental results leading to reinterpretation of spectral features.Comment: To appear in Phy. Rev. Let

Electron-spectroscopic investigation of metal-insulator transition in Sr2Ru1-xTixO4 (x=0.0-0.6)

We investigate the nature and origin of the metal-insulator transition in Sr2Ru1-xTixO4 as a function of increasing Ti content (x). Employing detailed core, valence, and conduction band studies with x-ray and ultraviolet photoelectron spectroscopies along with Bremsstrahlung isochromat spectroscopy, it is shown that a hard gap opens up for Ti content greater than equal to 0.2, while compositions with x<0.2 exhibit finite intensity at the Fermi energy. This establishes that the metal-insulator transition in this homovalent substituted series of compounds is driven by Coulomb interaction leading to the formation of a Mott gap, in contrast to transitions driven by disorder effects or band flling.Comment: Accepted for publication in Phys. Rev.

Carrier relaxation due to electron-electron interaction in coupled double quantum well structures

We calculate the electron-electron interaction induced energy-dependent inelastic carrier relaxation rate in doped semiconductor coupled double quantum well nanostructures within the two subband approximation at zero temperature. In particular, we calculate, using many-body theory, the imaginary part of the full self-energy matrix by expanding in the dynamically RPA screened Coulomb interaction, obtaining the intrasubband and intersubband electron relaxation rates in the ground and excited subbands as a function of electron energy. We separate out the single particle and the collective excitation contributions, and comment on the effects of structural asymmetry in the quantum well on the relaxation rate. Effects of dynamical screening and Fermi statistics are automatically included in our many body formalism rather than being incorporated in an ad-hoc manner as one must do in the Boltzman theory.Comment: 26 pages, 5 figure

SOUVENIR ALL INDIA COORDINATED RESEARCH PROJECT FOR DRYLAND AGRICULTURE CRIDA, HYDERABAD XV Working Group Meeting (24th-27th December, 2015) BISWANATH CHARIALI CENTRE ASSAM AGRICULTURAL UNIVERSITY

Not AvailableIt is my proud privilege to express heartfelt thanks to the entire AICRPDA family for giving me the responsibility of bringing out a souvenir to commemorate the occasion of XVth Working Group Meeting of AICRPDA at Biswanath Chariali Centre, BNCA, Assam Agricultural University. I, on behalf of the editorial board do extend a warm welcome to all delegate scientists and dignitaries coming from different parts of our country to this holy historic place of Biswanath, popularly known as ‘Gupta Kanshi’. Holding such a mega event of national importance for the first time at a place like Biswanath Chariali at the far east of the country amidst the bounty of natural resources and an area being almost entirely rainfed is of great significance. In view of the aim of realizing the dream of another green revolution that is envisaged from the rainfed areas of the country particularly the eastern and north eastern parts; this workshop is expected to march ahead further for achieving the goal. The vast ‘Gene’ resource of the North East India offers plenty of scope for their utilization to cope up the challenges of rainfed agriculture. This is a challenging task of converting these ‘Gene’ resources into viable ‘Seed Resources’ for their commercial exploitation keeping the very natural resource base and integrity unaltered. A holistic effort with all modern technological interventions is the need of the hour to bring into sustainable utilization of the natural resource base of the region. The idea of bringing out the souvenir in its present form came with the realization of the need of accumulating the multitude of the concepts required for framing the objectives of rainfed area research particularly for the North Eastern part of India. I am fortunate to have the wholehearted response from many luminaries from several ICAR institutes including CRIDA and number dignified scientists from the Assam Agricultural University contributing their valuable articles. I, do express gratitude and thankfulness from my inner core of the heart to all of them for their valuable contributions. I am extremely grateful to the Honorable Vice Chancellor, AAU, Dr. Kamalmalla Bujarbaruah sir, for his constant inspiration and suggestions all along the organization of the workshop. I would also like to express my sincere gratitude to Dr. Srinivasa Rao, Director, CRIDA, Dr. G. N. Hazarika, Director of Research (Agri), AAU, Dr.G.Rabindra Charry, PC, AICRPDA, Dr. T.C. Baruah, Associate Dean, BNCA, Dr. P.K. Sarma, CS, AICRPDA and all associated scientists for their encouragement, moral support and valuable suggestions. Last but not the least, all the Research Associates working under AICRPDA, BNCA, do deserve due share of thanks for their all round helps in bringing out the souvenir.Not Availabl

X-ray photoemission study of NiS_{2-x}Se_x (x = 0.0 - 1.2)

Electronic structure of NiS_{2-x}Se_x system has been investigated for various compositions (x) using x-ray photoemission spectroscopy. An analysis of the core level as well as the valence band spectra of NiS_2 in conjunction with many-body cluster calculations provides a quantitative description of the electronic structure of this compound. With increasing Se content, the on-site Coulomb correlation strength (U) does not change, while the band width W of the system increases, driving the system from a covalent insulating state to a pd-metallic state.Comment: 19 pages, 6 figures, To appear in Phys. Rev. B, 200

Regge behaviour of distribution functions and t and x-evolutions of gluon distribution function at low-x

In this paper t and x-evolutions of gluon distribution function from Dokshitzer-Gribov-Lipatov-Altarelli-Parisi(DGLAP) evolution equation in leading order(LO) at low-x, assuming the Regge behaviour of quark and gluon at this limit, are presented. We compare our results of gluon distribution function with MRST 2001, MRST 2004 and GRV '98 parameterizations and show the compatibility of Regge behaviour of quark and gluon distribution functions with perturbative quantum chromodynamics(PQCD) at low-x. We also discuss the limitations of Taylor series expansion method used earlier to solve DGLAP evolution equations, in the Regge behaviour of distribution functions.Comment: 19 pages, 7 figure