| Author: | Suen, Chun Hung |
| Title: | Electrical and magneto-transport properties of ZrTe2 thin films and its heterostructures |
| Advisors: | Dai, J. Y. (AP) |
| Degree: | Ph.D. |
| Year: | 2023 |
| Subject: | Transition metal compounds Two-dimensional materials Thin films Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Applied Physics |
| Pages: | xvi, 118 pages : color illustrations |
| Language: | English |
| Abstract: | As a class of quantum materials, topological insulators have shown fascinating electrical, magnetic and thermoelectric transport properties, making them great potential for applications in spintronic devices and topological quantum computers. Beyond many discovered group IVB chalcogenides topological materials, such as HfTe5 and ZrTe5, transition metal dichalcogenide (TMD) ZrTe2 is also recently predicted to be topological crystalline insulator, and has shown interesting properties in its thin film heterostructures such as massless Dirac fermions in ZrTe2/InAs. In this thesis work, electrical, magnetic and thermoelectric transport properties of ZrTe2 thin films and their heterostructures are investigated. By inspecting the magnetic characteristics of the ZrTe2 thin films on ferrimagnetic insulator YIG (Y3Fe5O12, yttrium iron garnet), high-temperature anomalous Hall effect (AHE) was demonstrated. In this heterostructure, significant anomalous Hall effect can be observed at temperatures up to at least 400 K, which is a record high temperature for the observation of AHE in TMDs, and the large RAHE is more than 1 order of magnitude larger than those previously reported values in topological insulators or TMD-based heterostructures. The magnetization of interfacial reaction-induced ZrO2 and YIG is believed to play a crucial role in the induced high-temperature AHE in the ZrTe2. Electrical transport properties of a ZrTe2/SrTiO3 (STO) heterostructure fabricated by pulsed laser deposition was studied. The remarkable Shubnikov-de Haas oscillations detected by angular-dependent magnetotransport measurements reveal clear evidence of a high mobility quasi-2DEG in the STO-based interface. Moreover, evidence for extra carriers with three-dimensional features was observed implying the multiband contributions, providing an explanation for some anomalous behavior in STO-based heterostructures. In addition, the thickness dependence study suggests the charge transfer effect between the capping metallic topological material ZrTe2 and the interfacial 2DEG. High-resolution transmission electron microscopy and electron energy loss spectroscopy results reveal interfacial structure and reaction. In the study of ZrTe2 thin film’s thermoelectric performances, a mechanism and device performance of enhanced thermoelectric performance induced by interfacial effect in a TMD-STO heterostructure was demonstrated. Owing to the formed conductive interface and elevated conductivity, the ZrTe2/STO heterostructure presents a large thermoelectric power factor of 3.7 × 105 𝜇𝑊𝑐𝑚−1𝐾−2 at 10 K. Formation of quasi-two-dimensional conductance at the interface is attributed for the large Seebeck coefficient and high electrical conductivity, leading to high thermoelectric performance which was demonstrated by a prototype device attaining 3 K cooling with 100 mA current input to this heterostructure. These results present a promising candidate for the spintronic, electronic and thermoelectric device applications. It may shed light on the designing approach to introduce magnetism to TMDs at room temperature. Also this thesis work provides insight into the intrinsic electronic structure of STO-based heterostructures, and the integrated systems can serve as a platform for studying the interplay of the 2DEG with attractive materials as well as developing practical thermoelectric and electronic devices. |
| Rights: | All rights reserved |
| Access: | open access |
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