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Strongly correlated materials are characterised by a complex electronic structure around the Fermi level, often consisting of Van Hove singularities (vHs) within a few meV. These are responsible for diverging points in the density of states that enhance electron correlations, creating instabilities that can lead to the emergence of superconductivity, ferromagnetism, metamagnetism and quantum criticality. The members of the Ruddlesden-Popper series of the strontium ruthenates are materials where the proximity of vHs to the Fermi level seems to be determinant for the observed electronic properties.
In this talk, I will focus on the ferromagnetic Sr4Ru3O10. By combining angle-resolved photoemission spectroscopy and scanning tunnelling microscopy (STM), we identify a rich hierarchy of vHs around the Fermi level. We find a saddle-point vHs just below the Fermi level, created by a spin-orbit coupling gap between a heavy spin-majority and a light spinminority bands. We develop a minimal tight-binding model that allowed us to identify a new mechanism for driving magnetic field induced Lifshitz transitions.
By sweeping the magnetic field between different polarizations, we demonstrate independent switching of the surface and bulk magnetizations in Sr4Ru3O10, leading to ferromagnetic and antiferromagnetic configurations. We identify this switching by abrupt changes to the electronic structure between the two configurations, revealed by scanning tunnelling spectroscopy. Using STM-based magnetostriction measurements, we directly detect the impact of the exchange interaction between the surface layer and the bulk of the material.
Dr. Carolina Marques completed her Ph.D. at the University of St Andrews in 2021, working in the group of Prof. Peter Wahl. She continued as a postdoctoral researcher at the University of St Andrews in 2021-2022. Her research has focused on studying the strongly correlated electronic states stabilized at the surface of strontium ruthenates by quasiparticle interference using scanning tunnelling microscopy. Since October 2022, she has been a postdoctoral researcher in the group of Prof. Fabian Natterer at the University of Zurich, where she has been using fast-quasiparticle interference techniques to probe the correlated states of 2D materials.
Zoom Meeting link: https://zoom.us/j/91830722165?pwd=ZEEwT3k4ZitVSnFtVGZBK3VkbFhSUT09
Meeting ID: 918 3072 2165 Password: 123456