Cascade of Fermi surface reconstructions inside the CDW phase of TiSe2
Microstructured Quantum Matter Seminar
- Date: Sep 7, 2022
- Time: 03:00 PM - 04:00 PM (Local Time Germany)
- Speaker: Roemer Hinlopen
- University of Bristol
- Location: CFEL (Bldg. 99)
- Room: Seminar Room I-III, Foyer
- Host: Carsten Putzke
The Fermi surface reconstruction induced by a charge density wave (CDW) has drawn interest for a long time. Recently, observations of CDW correlations in cuprates  and nickelates  have sparked new interest in CDW phases. Moreover, several scenarios for the relation to superconductivity have been proposed in high-temperature superconductors .
The transition metal dichalcolgenides have been instrumental in the development of CDW models as well as studies of Fermi surface reconstruction  and the interplay of CDWs with superconductivity . I will present our group’s recent studies of the Fermi surface evolution of TiSe2 with pressure over the entire CDW phase. We find a marked reduction in the critical pressure in the presence of non-hydrostaticity, owing to the delicate nature of these Van der Waals compounds . Furthermore, our quantum oscillation experiments reveal not only a reconstruction upon entering the CDW phase, but also a cascade of further Fermi surface reconstructions within the CDW phase.
To understand these transitions, we conducted DFT calculations to model the pressure evolution of the Fermi surface and find good agreement with our measurements. The obtained model suggests ambient pressure TiSe2 is a semi-metal  and suggests a link between the presence of a large Fermi surface pocket and superconductivity in TiSe2. These results provide a basis to quantitatively understand the interplay between CDW phases and electronic degrees of freedom which give rise to superconductivity.
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Roemer received his Masters degree from Radboud University in Nijmegen (Netherlands). He was an intern as well as a master student at the HFML Nijmegen where he performed measurements in high static magnetic fields. Currently, Roeer is a PhD student at the University of Bristol.
Some of his recent work is concerned with the magneto-transport properties of strange metals (https://arxiv.org/abs/2201.03292).