Universität zu Köln

Lippertz, Gertjan ORCID: 0000-0002-4061-7027 (2023). The Quantum Anomalous Hall Effect in Magnetically Doped Topological Insulators - A Study of the Current-Induced Breakdown. PhD thesis, Universität zu Köln.

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Abstract

The hallmark of the quantum anomalous Hall effect (QAHE) is its dissipationless chiral 1D state running along the edge of the quasi-2D magnetic-topological-insulator thin film, resulting in a vanishing longitudinal resistance and quantized Hall resistance equal to h/e^2. However, when reducing the device dimensions or increasing the current density, an abrupt breakdown of the dissipationless state occurs with a relatively small critical current. It is well-known that Coulomb disorder plays a strong role in compensated topological-insulators as a consequence of the random distribution of charged impurities. In regions with large uncompensated charge, metallic n- or p-type 'puddles' are formed. In this thesis, the electric-field-driven percolation of such 2D charge puddles in the gapped surface states of the quantum-anomalous-Hall-insulator (QAHI) thin films is proposed as the most likely cause of the breakdown of the QAHE. Although generally it is desirable to avoid breakdown, the chiral nature of the edge states gives rise to rectification (nonreciprocal) effects when the ideal QAHI-state is lost. In this thesis, the nonreciprocal charge transport in QAHIs is studied over a large parameter space of different temperatures, applied magnetic fields, electrostatic gate-potentials, and probe currents. Two distinct regimes are identified. At high currents and/or temperatures where Coulomb disorder only plays a minor role, the current-voltage relation follows the well-known quadratic current-dependence of nonreciprocal systems. However, at ultra-low temperatures when the current amplitude is decreased to only slightly exceed the critical current for breakdown, the description of the nonreciprocal charge transport becomes more complex. In this regime, the finite nonreciprocal response when the chemical potential lies inside the exchange gap is argued to be determined by the majority 2D charge puddles resulting from an imperfect charge compensation.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Lippertz, Gertjan gertjan.lippertz@gmail.com orcid.org/0000-0002-4061-7027 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-736823
Date:	2023
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics II
Subjects:	Natural sciences and mathematics Physics
Uncontrolled Keywords:	Keywords Language quantum anomalous Hall effect English QAHE English quantum anomalous Hall insulator English QAHI English magnetic topological insulator English breakdown English puddles English rectification English nonreciprocal charge transport English
Date of oral exam:	12 May 2023
Referee:	Name Academic Title Ando, Yoichi Prof. Dr. Pereira, Lino M. C. Prof. Dr. Cocolios, Thomas E. Prof. Dr. Van Bael, Margriet Prof. Dr. Bocquillon, Erwann Prof. Dr. Houssa, Michel Prof. Dr. Van Haesendonck, Chris Prof. Dr. Vantomme, André Prof. Dr. Assaf, Badih A. Prof. Dr.
Related URLs:	https://kuleuven.limo.libis.be/discovery...
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/73682