Spectroscopic perspectives on ultrafast coupling phenomena in perovskite oxides

In this thesis, I study ultrafast dynamics in perovskite oxides using time resolved broadband spectroscopy. I focus on the observation of coherent phonon propagation by time resolved Brillouin scattering: following the excition of metal transducer films with a femtosecond infrared pump pulse, coherent phonon dynamics in the GHz frequency range are triggered. Their propagation is monitored using a delayed white light probe pulse. The technique is illustrated on various thin films and multilayered samples. I apply the technique to investigate the linear and nonlinear acoustic response in bulk SrTiO_3, which displays a ferroelastic phase transition from a cubic to a tetragonal structural phase at T_a=105 K. In the linear regime, I observe a coupling of the observed acoustic phonon mode to the softening optic modes describing the phase transition. In the nonlinear regime, I find a giant slowing down of the sound velocity in the low temperature phase that is only observable for a strain amplitude exceeding the tetragonality of the material. It is attributed to a coupling of the high frequency phonons to ferroelastic domain walls in the material. I propose a new mechanism for the coupling of strain waves to the domain walls that is only effective for high amplitude strain. A detailed study of the phonon attenuation across a wide temperature range shows that the phonon attenuation at low temperatures is influenced by the domain configuration, which is determined by interface strain. Preliminary measurements on magnetic-ferroelectric multilayers reveal that the excitation fluence needs to be carefully controlled when dynamics at phase transitions are studied.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Potsdam

Year

2015

Author dc:creator

• Maerten, Lena

Contributors dc:contributor

• Bargheer, Matias

• coherent phonons
• phonon dynamics
• time resolved
• Brillouin scattering
• perovskite oxides
• optical spectroscopy
• hypersound propagation
• phonon damping
• domain wall motion
• phonon backfolding
• superlattice dispersion
• kohärente Phononen
• Phononen Dynamik
• zeitaufgelöst
• Brillouin Streuung
• Perowskit-Oxide
• optische Spektroskopie
• Hyperschall Propagation
• Phononen Dämpfung
• Domänenwandbewegung
• Phononen Rückfaltung
• Übergitter Dispersion

Statement dc:rights

• Keine öffentliche Lizenz: Unter Urheberrechtsschutz

Repository record source_url

https://publishup.uni-potsdam.de/frontdoor/index/index/docId/7762

OAI identifier oai:identifier

oai:kobv.de-opus4-uni-potsdam:7762