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  Dynamics of electronic order in Magnetoresistive Manganites studied with time-resolved x-ray scattering

Ehrke, H. P. (2011). Dynamics of electronic order in Magnetoresistive Manganites studied with time-resolved x-ray scattering. PhD Thesis, University of Oxford, Oxford.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0001-DB3F-3 Version Permalink: http://hdl.handle.net/21.11116/0000-0001-DB40-0
Genre: Thesis

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Thesis-HenriEhrke-Feb2011.pdf (Publisher version), 3MB
 
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Webseite "Quantum Condensed Matter Dynamics"-Department

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 Creators:
Ehrke, Henri P.1, Author              
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1Condensed Matter Dynamics Division, Max Planck Research Department for Structural Dynamics, Department of Physics, University of Hamburg, External Organizations, ou_2173637              

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 Abstract: This thesis presents studies on how photoexcitation disturbs the o rdering of the elec- tronic degree of freedom located at the manganese 3 d orbitals. Throughout the thesis the model compound La 0 . 5 Sr 1 . 5 MnO 4 has been studied. This material exhibits two di- mensional ordering of the charges and the orbitals (COO) and at a lo wer temperature also a three dimensional antiferromagnetic spin order. In the first approach the sample was photoexcited at 560 nm and th e ensuing dynamics was probed through the optical anisotropy at 630 nm. To this end two independent tunable noncollinear optical parameteric amplifiers (NO PA) were used. The cross correlation between them was measured to be 16 fs, muc h shorter than what previously has been used. The majority of the COO signal at 25 K was found to disappear with a time constant limited by the time-integral of the c ross correlation between pump and probe pulse. This hints towards an electrically-dr iven melting of the COO. To be more sensitive to the photo-induced changes in the COO, the t echnique of resonant soft x-ray diffraction was transferred from the static to the time-resolved domain. A diffractometer has been designed, built and comissioned wh ich allows time-resolved experiments on the single-layered manganite La 0 . 5 Sr 1 . 5 MnO 4 . In this way it was possible to separate the dynamics of the orbital from the spin ordering by measuring the intensities of the associated diffraction peaks. The time resolution was as good as 10 ps. On this timescale the orbital peak responded profoundly differently compared to the magnetic order ing peak. It was found that it is possible to melt the magnetic peak completely within the time resolu- tion, while the orbital ordered peak was much less affected. Throug h calculation and careful comparison with static data a temperature-driven effect could be excluded. Therefore, the experiments suggest that the quenching of the m agnetic order is an electrically-driven process.

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Language(s): eng - English
 Dates: 20112011
 Publication Status: Published in print
 Pages: 125
 Publishing info: Oxford : University of Oxford
 Table of Contents: -
 Rev. Type: -
 Identifiers: -
 Degree: PhD

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