Description of the thesis topic

Magnetotransport in magnetic topological insulator monolayers MnBi2Te4:
Toward a Quantum Anomalous Hall device for metrology
Background:
The concept of topological phase transition (awarded the Nobel prize for physics in 2016) has triggered
intensive research in fundamental physics as well as in applied research in the last 20 years, touching
fields as various as material research, optics, electronics, and metrology. In condensed matter,
topological systems are characterized by intrinsically metallic interface states surrounding an
insulating bulk. While 2D topological phases, such as the Quantum Hall effect (QHE), have metallic 1D
edge channels around an insulating surface, 3D topological insulators (3DTI, such as the Bi2Se3-Bi2Te3
family) display on their surface 2D metallic surface states with fascinating properties (helical spintexture and linear band structure similar to that of graphene).
Recently, a new type of topological system, the magnetic 3DTI MnBi2Te4, has been discovered. Beyond
surface states, MnBi2Te4 has been shown to display the Quantum anomalous Hall effect (QAHE) with
quantized conductance of 𝑒2/ℎ, similar to the QHE (at the basis of modern quantum metrology since
2019) – but stable without magnetic field. In this system, the interplay between topology, magnetism
and electronic property remains largely to investigate. Understanding this interplay will help
understand how to strengthen the QAHE up to application-relevant conditions for next-generation
quantum metrology.
Project objectives:
The goal of the PhD is to study the electronic properties of MnBi2Te4 nanostructures, and explore the
link between electronic, magnetic, and topological properties, through electrical transport
measurements at low temperature (down to 1.5K) and very high magnetic fields (60-90T). Thin
MnBi2Te4films are grown by collaborators at the University of Würzburg, with thicknesses ranging from
several tens of nm down to a single monolayer. The nanofabrication can be carried out in a research
cleanroom at IFW-Dresden. For magnetotransport, the LNCMI is one of four labs in the world where
magnetic fields as high as 90T are available, enabling to do Landau level spectroscopy on MnBi2Te4.
During this project, the PhD student will join a dynamic research network on magnetic TI between
Toulouse, Dresden, Würzburg and Grenoble and will be associated to every step of this research:
- prepare nanostructures of MnBi2Te4 thin films through laser and e-beam lithography (at IFW)
- study magnetotransport in MnBi2Te4 down to the monolayer in very high magnetic field (at LNCMI)
- analyze and understand their data, compare it with models
- present their study in research articles and at national/international conferences.

Work Context

-As part of an international collaboration between the LNCMI-Toulouse (France) and the IFW-Dresden
(Germany), a PhD position (and M2 internship potentially preceding it) is open at LNCMI, for a PhD
starting date ideally before 10.2025. The project is a fundamental study of the intrinsic properties of
magnetic topological insulators, a fascinating electronic phase of matter recently discovered which
demonstrated potential for quantum metrology.
Details on the PhD:
M2 internship: as a pre-PhD internship (preferred but non-mandatory)
Funding: fully funded position through the French-German ANR-DFG project IMAGIN
Location: LNCMI, Toulouse. As the PhD will be in co-tutelle with the IFW-Dresden, regular research
stays (up to a part of the PhD) is planned at IFW (especially for nanofabrication) – to be discussed.
Duration: 3 years (regulatory duration of a PhD thesis in France. Applicants must hold a Master degree)

Constraints and risks

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Additional Information

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