Photoemission study of exotic quantum states in ZrTex and development of new spin-resolved spectrometer
Abstract/Contents
- Abstract
- Zr-Te compounds is a very interesting family of materials, with a great many stable stoichiometry and different lattice structures. Known for its large thermopower, resistivity anomaly, and recent discovery of superconductivity under high pressure, ZrTe5 3D crystal has been predicted to be near the transition boundary between weak and strong topological insulator (TI), offering a promising platform to study topological phase transition. The existence of a gap and the existence of topological surface state (TSS) are two critical criteria to make such a categorization. However, different previous studies have reported discrepant results. Using 6eV-laser-based ARPES, I have performed a high-momentum-resolution and photon-energy-dependent measurement on ZrTe5. My experiment gives a defining quantification of the gap size and reconciles the discrepancies of previous works regarding the TSS, suggesting ZrTe5 not a 3D strong TI. With a different stoichiometry, ZrTe2 not only exhibits a significantly different lattice structure, but shows a more exciting physics than ZrTe5 as well. Recently, charge density wave (CDW) has been observed in monolayer (ML) form ZrTe2. Given that there has been no work officially reporting CDW in bulk ZrTe2, it is important to understand whether the CDW in ZrTe2 ML is lattice-driven or exciton-driven, the latter of which indicates a new platform to study excitonic insulator. One way to distinguish the two scenarios is to see the ultrafast response of the system. Using femtosecond-resolved 6+1.5 eV pump-probe ARPES, I have observed the ultrafast disappearing of CDW folded band at Gamma point in ZrTe2 ML, which shows a time scale much faster than what is expected to be a lattice-driven CDW, indicating that CDW in ZrTe2 ML is contributed by exciton. Tuning knobs like photon-energy and ultrafast snapshot reveal us important information of quantum materials; are we able to observe spin-dependent phenomena? Traditional way to detect spin is to use a Mott detector attached to a hemispherical analyzer, which is commercially available but has very low spin-resolving efficiency and low data-acquisition throughput. Therefore, in parallel to my scientific exploration, I have been developing a next-generation spin-resolved ARPES using time-of-flight (TOF) method to detect kinetic energy and low-energy exchange (LEX) scattering to detect spin, with a significant improvement of both efficiency and resolution. A deflection mapping capability with different focusing modes is also incorporated. After a series of experiments and simulations, I conclude that the newly developed spin-TOF spectrometer achieves a comparable energy and angular resolution compared to the state-of-the-art spin-ARPES setup.
Description
| 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 | 2018; ©2018 |
| Publication date | 2018; 2018 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Xiong, Hongyu |
|---|---|
| Degree supervisor | Shen, Zhi-Xun |
| Thesis advisor | Shen, Zhi-Xun |
| Thesis advisor | Devereaux, Thomas Peter, 1964- |
| Thesis advisor | Heinz, Tony F |
| Degree committee member | Devereaux, Thomas Peter, 1964- |
| Degree committee member | Heinz, Tony F |
| Associated with | Stanford University, Department of Applied Physics. |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Hongyu Xiong. |
|---|---|
| Note | Submitted to the Department of Applied Physics. |
| Thesis | Thesis Ph.D. Stanford University 2018. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2018 by Hongyu Xiong
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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