Studying the electronic structure of the polar surfaces of delafossites using μ-ARPES
Abstract
This thesis presents the results of my angle-resolved photoemission (ARPES) study of the delafossite oxides PdCoO₂, PtCoO₂ and PdCrO₂ as well as delafossite-like AgCrSe₂. When cleaving the sample, their layered ABX₂ structure results in distinct surface terminations that are spatially distributed across the sample. These are either electron (A-termination) or hole doped (BX₂-termination) with respect to the bulk, resulting in their markedly different surface electronic structures. These electronic surface structures host a delicate interplay between the spin-, charge-, and orbital-degrees of freedom, driving the formation of new phases. The understanding of this interplay is the central concept of this thesis.
Probing defined surface domains has often been challenging due to the beam spot of the incoming light being larger than a single domain. Here, I show that by using μ-ARPES, where the beam spot is focused to 4 μm, it is possible to probe the electronic structure of a distinct surface termination and study the extent of spatial variations in the electronic structure across the sample. Identifying areas of pristine terminations greatly increased the effective resolution, enabling the detailed study of the surface electronic structure. I show that PdCrO₂ undergoes a charge-order driven surface reconstruction that protects the insulating nature of the CrO₂ states at the surface. For PdCoO₂, I demonstrate strong electron-phonon coupling on both the CoO₂- and Pd-terminated surfaces, with an unusually strong coupling on the Pd-termination driving the formation of two distinct polaron modes. I conclude by presenting my study on non-centrosymmetric delafossite-like AgCrSe₂. Here, a delicate interplay between bulk and surface inversion symmetry breaking results in a Rashba-type splitting of the states derived from different magnetic domains. I will also revise the role of the subsurface layer for these systems which has thus far been widely neglected but is crucial to achieve an accurate description of the underlying physics.
Type
Thesis, PhD Doctor of Philosophy
Rights
Creative Commons Attribution-NonCommercial 4.0 International
http://creativecommons.org/licenses/by-nc/4.0/
Embargo Date: 2026-04-30
Embargo Reason: Thesis restricted in accordance with University regulations. Restricted until 30 April 2026
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Description of related resources
Studying the electronic structure of the polar surfaces of delafossites using mu-ARPES (thesis data) Siemann, G., University of St Andrews, 30 Apr 2026. DOI: https://doi.org/10.17630/76a9903a-e957-4c42-94d6-864f91a63371Antonelli, T., Rajan, A., Watson, M. D., Soltani, S., Houghton, J., Siemann, G.-R., Zivanovic, A., Bigi, C., Edwards, B. M., & King, P. (2024). Controlling the charge density wave transition in single-layer TiTe2xSe2(1−x) alloys by band gap engineering. Nano Letters, 24(1), 215-221. Article 3c03776. https://doi.org/10.1021/acs.nanolett.3c03776 [https://hdl.handle.net/10023/28921 : Open Access version]
Siemann, G.-R., Kim, S.-J., Abarca Morales, E., Murgatroyd, P., Zivanovic, A., Edwards, B. M., Markovic, I., Mazzola, F., Trzaska, L., Clark, O. J., Bigi, C., Zhang, H., Achinuq, B., Hesjedal, T., Watson, M. D., Kim, T. K., Bencok, P., van der Laan, G., Polley, C. M., ... King, P. (2023). Spin-orbit coupled spin-polarised hole gas at the CrSe2-terminated surface of AgCrSe2. npj Quantum Materials, 8, Article 61. https://doi.org/10.1038/S41535-023-00593-4 [https://hdl.handle.net/10023/28614 : Open Access version]
de Almeida Marques, C., Murgatroyd, P., Fittipaldi, R., Osmolska, W., Edwards, B. M., Benedicic, I., Siemann, G.-R., Rhodes, L. C., Buchberger, S., Naritsuka, M., Abarca Morales, E., Halliday, D. R., Polley, C., Leandersson, M., Horio, M., Chang, J., Arumugam, R., Lettieri, M., Granata, V., ... Wahl, P. (2024). Spin-orbit coupling induced Van Hove singularity in proximity to a Lifshitz transition in Sr4Ru3O10. npj Quantum Materials, 9, Article 35. https://doi.org/10.1038/s41535-024-00645-3 [https://hdl.handle.net/10023/29630 : Open Access version]
Edwards, B., Dowinton, O., Hall, A., Murgatroyd, P., Buchberger, S., Antonelli, T., Siemann, G.-R., Rajan, A., Abarca Morales, E., Zivanovic, A., Bigi, C., Belosludov, R., Polley, M., Carbone, D., Mayoh, D., Balakrishnan, G., Bahramy, M., & King, P. (2023). Giant valley-Zeeman coupling in the surface layer of an intercalated transition metal dichalcogenide. Nature Materials, 22(4), 459-465. https://doi.org/10.1038/s41563-022-01459-z [https://hdl.handle.net/10023/26790 : Open Access version]
Abarca Morales, E., Siemann, G.-R., Zivanovic, A., Murgatroyd, P., Markovic, I., Edwards, B., Hooley, C., Sokolov, D., Kikugawa, N., Cacho, C., Watson, M., Kim, T., Hicks, C. W., Mackenzie, A., & King, P. (2023). Hierarchy of Lifshitz transitions in the surface electronic structure of Sr2RuO4 under uniaxial compression. Physical Review Letters, 130(9), Article 096401. https://doi.org/10.1103/PhysRevLett.130.096401 [https://hdl.handle.net/10023/26774 : Open Access version]
Bigi, C., Qiao, L., Liu, C., Barone, P., Hatnean, M. C., Siemann, G.-R., Achinuq, B., Mayoh, D. A., Vinai, G., Polewczyk, V., Dagur, D., Mazzola, F., Bencok, P., Hesjedal, T., van der Laan, G., Ren, W., Balakrishnan, G., Picozzi, S., & King, P. D. C. (2023). Covalency, correlations, and interlayer interactions governing the magnetic and electronic structure of Mn3Si2Te6. Physical Review. B, Condensed matter and materials physics, 108(5), Article 054419. https://doi.org/10.1103/PhysRevB.108.054419 [https://hdl.handle.net/10023/28543 : Open Access version]
Baenitz, M., Piva, M. M., Luther, S., Sichelschmidt, J., Ranjith, K. M., Dawczak-Dȩbicki, H., Ajeesh, M. O., Kim, S. .-J., Siemann, G., Bigi, C., Manuel, P., Khalyavin, D., Sokolov, D. A., Mokhtari, P., Zhang, H., Yasuoka, H., King, P. D. C., Vinai, G., Polewczyk, V., ... Schmidt, M. (2021). The planar triangular S = 3/2 magnet AgCrSe2: magnetic frustration, short range correlations, and field tuned anisotropic cycloidal magnetic order. Physical Review. B, Condensed matter and materials physics, 104(13). https://doi.org/10.1103/PhysRevB.104.134410 [https://hdl.handle.net/10023/23994 : Open Access version]
Watson, M. D., Rajan, A., Antonelli, T., Underwood, K., Marković, I., Mazzola, F., Clark, O. J., Siemann, G.-R., Biswas, D., Hunter, A., Jandura, S., Reichstetter, J., Mclaren, M., Le Fèvre, P., Vinai, G., & King, P. D. C. (2020). Strong-coupling charge density wave in monolayer TiSe2. 2D Materials, 8(1), Article 015004. https://doi.org/10.1088/2053-1583/abafec [https://hdl.handle.net/10023/24111 : Open Access version]
Related resources
https://doi.org/10.17630/76a9903a-e957-4c42-94d6-864f91a63371https://hdl.handle.net/10023/28921
https://hdl.handle.net/10023/28614
https://hdl.handle.net/10023/29630
https://hdl.handle.net/10023/26790
https://hdl.handle.net/10023/26774
https://hdl.handle.net/10023/28543
https://hdl.handle.net/10023/23994
https://hdl.handle.net/10023/24111
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