Dashwood, Cameron Darling;
(2022)
Characterisation and control of electron-lattice coupling in 4d and 5d quantum materials.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
The burgeoning field of quantum materials concerns systems that do not adhere to the traditional theories of condensed matter physics. A key feature of these materials is a strong coupling between structural, electronic and magnetic degrees of freedom, which is especially prominent in 4d and 5d transition- metal oxides. The consequences of this coupling are wide, stabilising a range of emergent phases that are sensitive to perturbation. In this thesis, I develop novel techniques based on neutron and x-ray scattering to characterise and control electron-lattice coupling in 4d and 5d quantum materials. I begin with Ca3Ru2O7, a 4d polar metal that hosts a spin-reorientation transition. Using neutron and resonant x-ray scattering, I reveal a new cy- cloidal magnetic phase, arising from spin-orbit coupling, that rapidly evolves with temperature to mediate the transition. I further show that the cycloid- mediated spin-reorientation can be driven by anisotropic strain, demonstrating the control enabled by coupling to the lattice. I then turn to resonant inelastic x-ray scattering (RIXS), which has re- cently received interest as a new probe of electron-phonon coupling (EPC). Using graphite as a model system, I demonstrate the power of RIXS to probe the momentum-dependent EPC for a range of excited electronic states. Our RIXS data reveal some key deficiencies of current theoretical models of phonon excitations in RIXS, and prompt the development of a new Green’s-function– based model by our collaborators to address these issues. Finally, I present a study of the 5d material Sr2IrO4, a famous jeff = 1/2 spin-orbit Mott insulator. I characterise the phonon spectrum with non- resonant inelastic x-ray scattering, before using RIXS to explore the phonon and magnon excitations. I find a strong EPC similar to that seen in the cuprates, and offer a new interpretation of the magnon dispersion involving coupling to spin-orbit excitons.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Characterisation and control of electron-lattice coupling in 4d and 5d quantum materials |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy UCL > Provost and Vice Provost Offices > UCL BEAMS UCL |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10150842 |
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