Designing quantum matter in two dimensions

Thumbnail Image
Files
isbn9789526412931.pdf (28.26 MB)
Journal Title
Journal ISSN
Volume Title
School of Science | Doctoral thesis (article-based) | Defence date: 2023-06-22
Unless otherwise stated, all rights belong to the author. You may download, display and print this publication for Your own personal use. Commercial use is prohibited.
Author
Date
2023
Department
Teknillisen fysiikan laitos
Department of Applied Physics
Major/Subject
Mcode
Degree programme
Language
en
Pages
58 + app. 64
Series
Aalto University publication series DOCTORAL THESES, 82/2023
Abstract
Experimental condensed matter research is experiencing a paradigm shift. In the past, the need for 3D crystalline samples with a specific structure and doping imposed strict requirements for achieving the desired properties. Now, it is possible to create tunable 2D samples in the lab, overcoming the previous limitations and accelerating the research. In this thesis, I will demonstrate how we utilized the molecular beam epitaxy (MBE) technique to design and fabricate van der Waals (vdW) heterostructures. The vdW nature of the MBE-grown materials enabled us to combine physical properties of different materials without altering them. I will showcase how we engineered two phases of matter that are central to condensed matter physics, and probed them using scanning tunneling microscope. The first is heavy fermions, which we artificially created by combining magnetic and metallic vdW materials. Here, a lattice of magnetic moments in 1T-TaS2 couples via the Kondo exchange coupling to conduction electrons in 1H-TaS2, resulting in the emergence of Kondo lattice physics. The flat band of Kondo lattice hybridized with the dispersive electrons, leading to a gap at the Fermi level of 1H-TaS2. In this special case of separated magnetic moments and conduction electrons, we reproduce the expected observables in the spectral function: Kondo peak on the side of magnetic lattice and heavy-fermion hybridization gap on the side of conduction electrons. The second is unconventional superconductivity, which we attempted to achieve in two different systems: a monolayer vdW material and a vdW heterostructure composed of a superconductor and a magnet. We observe strong signatures of nodal superconductivity in 1H-TaS2: V-shaped spectral gap, many-body fluctuations and a pseudogap, which is the first evidence of unconventional superconductivity in a monolayer vdW material. We also create topological superconductivity in a heterostructure of magnetic CrBr3 and superconducting 2H-NbSe2, and observe the edge state and the Shiba bands. Futhermore, we show that the topology of this system arises from the moiré pattern. These results highlight the benefits of the designer approach and open new opportunities in their respective fields.
Description
Supervising professor
Liljeroth, Peter, Prof., Aalto University, Department of Applied Physics, Finland
Keywords
scanning tunneling miscroscopy, correlated materials, topological matter, superconductivity, heavy fermions
Other note
Parts
  • [Publication 1]: Viliam Vaňo, Mohammad Amini, Somesh C. Ganguli, Guangze Chen, Jose L. Lado, Shawulienu Kezilebieke and Peter Liljeroth. Artificial heavy fermions in a van der Waals heterostructure. Nature, 599, 582–586, November 2021.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-2021120110512
    DOI: 10.1038/s41586-021-04021-0 View at publisher
  • [Publication 2]: Viliam Vaňo, Somesh Chandra Ganguli, Mohammad Amini, Linghao Yan, Maryam Khosravian, Guangze Chen, Shawulienu Kezilebieke, Jose L. Lado and Peter Liljeroth. Evidence of nodal f-wave superconductivity in monolayer 1H-TaS2 with hidden order fluctuations. Submitted to Nature Materials, October 2022
  • [Publication 3]: Shawulienu Kezilebieke, Md Nurul Huda, Viliam Vaňo, Markus Aapro, Somesh C. Ganguli, Orlando J. Silveira, Szczepan Głodzik, Adam S. Foster, Teemu Ojanen and Peter Liljeroth. Topological superconductivity in a van der Waals heterostructure. Nature, 588, 424–428, December 2020.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-2020123160458
    DOI: 10.1038/s41586-020-2989-y View at publisher
  • [Publication 4]: Shawulienu Kezilebieke, Orlando J. Silveira, Md N. Huda, Viliam Vaňo, Markus Aapro, Somesh C. Ganguli, Jouko Lahtinen, Rhodri Mansell, Sebastiaan van Dijken, Adam S. Foster and Peter Liljeroth. Electronic and Magnetic Characterization of Epitaxial CrBr3 Monolayerson a Superconducting Substrate. Advanced Materials, 33, 2006850, May 2021.
    DOI: 10.1002/adma.202006850 View at publisher
  • [Publication 5]: Shawulienu Kezilebieke, Viliam Vaňo, Md N. Huda, Markus Aapro, Somesh C. Ganguli, Peter Liljeroth and Jose L. Lado. Moiré-Enabled Topological Superconductivity. Nano Letters, 22, 328-333, January 2022.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202201261479
    DOI: 10.1021/acs.nanolett.1c03856 View at publisher
Citation
Permanent link to this item
https://urn.fi/URN:ISBN:978-952-64-1293-1
Collections
[diss] Perustieteiden korkeakoulu / SCI