Ultrafast dynamics beyond the average response : a case study of KTaO3 and SrTiO3

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Ultrafast light pulses offer a powerful means to drive materials into non-equilibrium states, unlocking novel properties that are often inaccessible in equilibrium conditions. In strongly coupled systems, such as the perovskite materials, macroscopic states such as paraelectricity, ferromagnetism, ferroelectricity, multiferroicity, and even superconductivity emerge, often accompanied by associated or competing structural transitions. Using ultrafast light pulses it is possible to dynamically modify the properties of these materials, aiming to drive them towards energetically related states. Recent advancements in free electron lasers enable the characterization of these states at all relevant length scales, which enables the development of techniques to dynamically control materials from the mesoscopic to the atomic scale. I first discuss the case of KTaO3 , which exhibits a ferroelectric instability as a soft mode at low temperatures, but quantum fluctuations prevent the occurrence of a ferroelectric transition. By dynamically modifying the electronic structure of KTaO3 through above-gap optical excitation, I then employ X-ray pulses to observe the resulting modified structure. My observations reveal the stabilization of the paraelectric phase and a notable hardening of the acoustic branch. Next, I investigate SrTiO3 , which also demonstrates a similar ferroelectric instability at low temperatures. Here, I used a single cycle THz pulse with the intention of driving the zone center ferroelectric soft mode and observing the emergence of ferroelectricity in SrTiO3 using X-ray pulses. Surprisingly, I do not observe an average unit cell response and instead observe nanoscale dynamics. Even more unusually, this nanoscale response is polar and inverts with the direction of the THz field. Overall, this research demonstrates the exciting potential of ultrafast light pulses in driving material transitions and exploring the dynamic properties of strongly coupled systems. The observed modifications and emergent phenomena in KTaO3 and SrTiO3 offer valuable insights into the nonequilibrium physics of materials, which serve as a foundation for the future design and development of novel materials.


Type of resource text
Form electronic resource; remote; computer; online resource
Extent 1 online resource.
Place California
Place [Stanford, California]
Publisher [Stanford University]
Copyright date 2023; ©2023
Publication date 2023; 2023
Issuance monographic
Language English


Author Krapivin, Viktor
Degree supervisor Reis, David A, 1970-
Thesis advisor Reis, David A, 1970-
Thesis advisor Bucksbaum, Philip H
Thesis advisor Hastings, Jerome, 1948-
Degree committee member Bucksbaum, Philip H
Degree committee member Hastings, Jerome, 1948-
Associated with Stanford University, School of Humanities and Sciences
Associated with Stanford University, Department of Applied Physics


Genre Theses
Genre Text

Bibliographic information

Statement of responsibility Viktor Krapivin.
Note Submitted to the Department of Applied Physics.
Thesis Thesis Ph.D. Stanford University 2023.
Location https://purl.stanford.edu/gf707vt0266

Access conditions

© 2023 by Viktor Krapivin
This work is licensed under a Creative Commons Attribution Share Alike 3.0 Unported license (CC BY-SA).

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