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Phononic and electronic excitations in complex oxides studied with advanced Infrared and Raman spectroscopy techniques

Breite Öffentlichkeit Verteidigung der Dissertation
16.07.2021 15:30

Promising candidates for next-generation devices are the transition metal-oxide perovskites (also called complex oxides), which host a plethora of novel physics, including emergent phases of spin, charge, orbital and structural origin. They are also often very susceptible to external perturbation parameters, yielding complex phase diagrams of these materials. Reducing the system’s length scale to the atomic level can further provide new exciting physics.
The macroscopic effects observed in these materials are governed, to a large extent, by the behavior of the phonons and electrons. Therefore, it is essential to study the low-energy dynamics of the material system. A suitable approach is optical spectroscopy, i.e. by using photons as a probe since they are non-destructive and non-invasive for lower energy ranges, yet they can trigger light-induced transitions at higher energies. They can also be polarized, thus providing important information on the symmetry of the material structure. Despite the great capability of optical spectroscopy, its real potential for investigating and controlling solid state systems has not been fully exploited.
This PhD work presents advanced infrared and Raman spectroscopy techniques in combination with various external stimuli, which have been used to obtain information on the low-energy electronic and phononic dynamics of several complex oxide systems in bulk form or as thin film heterostructures. In particular, the optical signatures of the magnetic-field-induced charge density wave in the underdoped high-temperature superconductor YBa2Cu3O6+x have been studied by means of THz-infrared reflectivity and up to 30 Tesla [1]. Secondly, confocal Raman spectroscopy was used to discover the emergence of backfolded acoustic phonons in metal-oxide superlattices, and demonstrate their high potential as a state of the art characterization tool for superstructures [2]. Finally, the electric field effect on SrTiO3- and KaTiO3-based heterostructures was explored using a unique combination of infrared ellipsometry and confocal Raman spectroscopy [3].

[1] Lyzwa et al. ‘Infrared spectroscopy study of the in-plane response of YBa2Cu3O6.6 in magnetic fields up to 30 Tesla’ Phys. Rev. Research 2, 023218 (2020)
[2] Lyzwa et al. ‘Backfolded acoustic phonons as ultrasonic probes in metal-oxide superlattices’
Phys. Rev. Materials 4, 043606 (2020)
[3] Lyzwa et al. ‘Asymmetric and non-collinear polar moments at back-gated SrTiO3 interfaces’ submitted (2021)

Wann? 16.07.2021 15:30
Wo? PER 08 0.51
Chemin du Musée 3
1700 Fribourg
Vortragende Fryderyk Lyzwa
Présentation publique de thèse de Doctorat
Kontakt Département de physique
Christian Bernhard
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