Project

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Theoretical support for resonant soft X-ray spectroscopy and related experiments at SLS

Applicant Delley Bernard
Number 129970
Funding scheme Project funding
Research institution Condensed Matter Theory Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Theoretical Physics
Start/End 01.04.2011 - 31.03.2013
Approved amount 216'891.00
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All Disciplines (3)

Discipline
Theoretical Physics
Physical Chemistry
Condensed Matter Physics

Keywords (8)

X-ray; spectroscopy; many-body; impurity; multiplet; Inelastic X-ray scattering; transition metals; electron correlations

Lay Summary (English)

Lead
Lay summary
Resonant scattering inelastic and elastic is an important tool in materials research at SLS.For challenging materials, such as transition metal compounds, it is necessary to have computational theory support for state of the art interpretation.With the retirement of two international leaders in the field such support might be dwindling. It is an opportunity to strengthen the support for these activities by the condensed matter theory group at PSI.For materials with intermediate electron correlations such as manganates, nickelates and cuprates even ground state theory is not settled today. In order to help PSI make significant contributions to the clarification of their electronic properties, we propose to enhance our capabilities to evaluate the predictions for the forefront approximate theories that are of relevance.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Atomic Multiplets in X-ray Spectroscopies of Solids
Delley Bernard, Uldry Anne-Christine (2013), Atomic Multiplets in X-ray Spectroscopies of Solids, in Bulletin of the American Physical Society, U23.00001.
Systematic computation of crystal-field multiplets for x-ray core spectroscopies
Uldry A, Vernay F, Delley B (2012), Systematic computation of crystal-field multiplets for x-ray core spectroscopies, in Physical Review , B85(12), 125133-1-125133-14.
Atomic Multiplets in X-ray spectroscopies revisited
Delley Bernard, Vernay Francois, Uldry Anne-Christine (2012), Atomic Multiplets in X-ray spectroscopies revisited, in Bulletin of the American Physical Society, APS March Meeting 2012 , H39.00004.

Collaboration

Group / person Country
Types of collaboration
Universite Perpignan France (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Stanford University United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
IFW Dresden Germany (Europe)
- Publication

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
CCP9 Networking Activity on High-Resolution Electron Microscopy and EELS 01.05.2013 Cambridge (UK)
Workshop Future challenges for the theory of x-ray spectroscopy 11.04.2013 Diamond Light Source, Didcot (UK)
American Physical Society march meeting 18.03.2013 Baltimore USA
Workshop on Fundamental Aspects of X-ray Spectroscopies 21.02.2013 Utrecht University NL
Annual Meeting of the Swiss Physical Society 21.06.2012 ETH Zürich
SPR-KKR Hands-on Course 2012 11.06.2012 Paul Scherrer Institute
Colloquium Physics 02.03.2012 USF Tampa
American Physical Society march meeting 27.02.2012 Boston USA
JUM@P'11: Second Joint Users' Meeting @ PSI 15.09.2011 PSI Villigen
Swiss Physical Society meeting 2011 15.06.2011 EPFL (CH)


Knowledge transfer events

Active participation

Title Type of contribution Date Place Persons involved
Workshop on Fundamental Aspects of X-ray Spectroscopies: the role of the 2p core hole in XAS and RIXS 21.02.2013 Utrecht University (NL)
SPR-KKR Hands-on Course 2012 11.06.2012 Paul Scherrer Institute


Associated projects

Number Title Start Funding scheme
109358 Time Dependent Density Functional Approach for Electron Spectroscopy of Surfaces 01.09.2006 Project funding
141962 Mott Physics Beyond the Heisenberg Model in Iridates and Related Materials 01.01.2013 Sinergia

Abstract

Resonant inelastic and elastic scattering (RIXS) is an important tool in materials researchat SLS. Because of the resonant character of the core excitation it yields elementspecific spectra with much higher intrinsic resolution than core absorption spectra.To measure such spectra aninvestment of about 5 MCHF was put in the ADDRESS beamline at SLS-PSI alone.Further similar, perhaps improved beamlines are under construction and planned elsewhere.For challenging materials, such as transition metal compounds, it is necessaryto have computational theory support for state of the art interpretation.With the retirement of two international leaders in the field (Kotani, Sawatzky)such support might be dwindling rather than expand.This gives an opportunity to strengthen thesupport for these activities by the condensed matter theory group at PSI.For materials with strong electron correlation effects such as manganates, nickelatesand cuprates even ground state theory is not settled today. In order to helpPSI to make significant contributions to the clarification of their electronic properties,we propose to enhance our capabilities to evaluate the predictions for theforefront approximate theories that are of relevance.In transition metal elements the soft X-ray resonance of greatest interest involves the L$_{2,3}$absorption edge of the X-ray absorption spectrum (XAS).The electron-electron interaction from open 2p core shell and theopen 3d shell lead to significant atomic multiplet splitting.This has been recognized long ago, and old computer programs for atomic states have beenadapted for high symmetry crystal fields. For most symmetries of the crystal environmentadaptation of these calculations is cumbersome and thus ignored.The atomic crystal field multiplet method developed by the proponent and collaboratormakes crystalline environments of arbitrary or even no symmetry easily accessible toexperimentalists and delivers a reasonably good prediction of XAS and RIXS spectrawith standard input on the two open shells and neighboring ions quasi ab initio.Considering the ion charges as parameters, as well as semi-empirical screening andcore hole lifetime, the method can be used for fitting experiments in a transparent way.The method is set up for XAS and RIXS calculations and can be extended forX-ray magnetic circular dichroism (XMCD) experiments and can also be extended to supplyuseful results for the analysis of soft X-ray resonant scattering.The challenges ahead, which are theme of this proposal, are clear.In view of the complex ground states of the d-element compounds, the assumption of a singled- configuration is oversimplified, especially if photoemission and similar spectra are to becovered too. In order to retain the simplicity of an approach without previous symmetryreduction of the crystal-field multiplet problem we will be lead to apply Lanczos spectral methods.This development is the core piece of the present proposal.Once this has been achieved, it should be possible to consider also simple ligandfields arising in cluster models with a few explicit neighbor atoms.At this point it is not clear if it will be possible to use such a method to couple toa band structure description of the surrounding crystal. If it will, this can benamed a low temperature, exact diagonalization method, for the full atomic multipletin a dynamic mean field theory.The main line of the planned research is to keep the tool in a state reasonably easilyaccessible to the experimentalist, so that the consequences of intra atomic electron-electroninteraction and its coupling to the environment can be readily inspected for anysubstance under investigation.
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