PhD defense: Magnetoresistance effects in topological and conventional systems
On Tuesday June 5th, 2018, Thomas Khouri will defend his doctorate thesis in the Aula of the Radboud University. During his PhD research at the HFML, he focused on the electrical properties of two-dimensional semiconductors and topological insulators.
A fundamental understanding of the electronic properties of solids is one of the main pillars for modern technology. During his PhD research, Thomas Khouri investigated low-dimensional electron systems in which the motion of charge carriers is restricted to two dimensions realized in GaAs and HgTe heterostructures and three-dimensional topological insulators by means of electrical transport at low temperatures and in high magnetic fields up to 37.5 T.
The two-dimensional (2D) electron system based on HgTe quantum wells has peculiar properties. Depending on the thickness of the quantum well, this system is either a narrow-gap semiconductor or a 2D topological insulator. In his magneto-transport experiments, Khouri investigated the Quantum Hall effect up to liquid nitrogen temperatures and studied the origin of the in-plane magneto-resistance in the topological phase in these systems. The samples have been grown and prepared in the laboratory of Laurens Molenkamp at the University of Würzburg.
The main part of his research focused on investigating magneto-resistance (MR) phenomena that are predominantly associated with exotic band structures or quasi-particles that behave like relativistic particles. His approach was to probe the MR in conventional GaAs heterostructures, grown in the Wegscheider Laboratory at the ETH Zürich. Khouri demonstrated in temperature-dependent transport experiments in these ultraclean systems in which charge carriers obey a parabolic energy-momentum relation, that density fluctuations cause a peculiar linear MR in a wide range of magnetic fields. With this work he showed that density fluctuations which are inevitably present in any material demystify the origin of linear MR. In his transport experiments on the three-dimensional topological insulator Bi2Se3, Thomas Khouri showed that another magneto-resistance phenomenon, the negative longitudinal magneto-resistance (NLMR), which is linked to quasi-particle properties in Weyl semimetals, can also be observed in a simple topological insulator. These examples demonstrate that the observation of peculiar magneto-resistance features has often a classical origin and does not need the association with exotic material properties.
Thomas Khouri (Naila, Germany, 1988) studied Physics at the University of Würzburg, Germany between 2007 and 2013. Between 2013 and 2017, he worked as PhD student at the HFML. Since November 2017, Thomas Khouri works as Post-Doctoral Researcher at the HFML in Nijmegen.
PhD defense: Magnetoresistance effects in topological and conventional systems
On Tuesday June 5th, 2018, Thomas Khouri will receive his doctorate degree in the Aula of the Radboud University. During his PhD research at the HFML, he focused on the electrical properties of two-dimensional semiconductors and topological insulators.
