Quantum Transport and Electric-Field Effects in Layered Topological Semimetals and Magnetic Materials
type: CreativeWork
description: This dissertation describes transport experiments on quantum devices in layered Dirac nodal line topological semimetals and antiferromagnetic materials down to a few layers. We used gate-induced effects to alter the transport properties of these materials. First, we introduced current annealing in topological semimetals to achieve high-quality devices. We demonstrate current annealing to substantially improve the electronic transport properties of 2D topological semimetal flakes. Contact resistance and resistivity were improved by factors up to 2,000,000 and 20,000, respectively, in devices based on exfoliated flakes of two topological semimetals, ZrSiSe and BaMnSb2. Using this method, carrier mobility in ZrSiSe improved by a factor of 3800, resulting in the observation of record-high mobility for exfoliated ZrSiSe. Quantum oscillations in annealed ZrSiSe appeared at magnetic fields as low as 5 T, and magnetoresistance increased by 10,000. We argue that a thermal process underlies this improvement. Finally, Raman spectroscopy and analysis of quantum oscillations in ZrSiSe indicate that the phonon modes and Fermi surface area are unchanged by current annealing. Through current annealing, we had access to suitable device quality, hence could investigate topological semimetals extensively. We studied Shubnikov de Haas oscillations focused on the unexpected frequency of 140 T that is unrelated to any known surface (450 T) or bulk (220 T) Fermi surface. We show that this frequency has a 2D nature by providing angle dependence and thickness dependence of quantum oscillations. Angle dependence of 140 T follows 1/cos(θ), in contrast to bulk frequency, 220 T, which shows no change with angle. In addition, thickness dependence shows that the relative amplitude of 140 T to 220 T exponentially increases by decreasing the thickness. In addition, we provide a comparison of phase analysis of 140 T with 220 T that shows the different origins of these frequencies. We speculate this …
abstract: This dissertation describes transport experiments on quantum devices in layered Dirac nodal line topological semimetals and antiferromagnetic materials down to a few layers. We used gate-induced effects to alter the transport properties of these materials. First, we introduced current annealing in topological semimetals to achieve high-quality devices. We demonstrate current annealing to substantially improve the electronic transport properties of 2D topological semimetal flakes. Contact resistance and resistivity were improved by factors up to 2,000,000 and 20,000, respectively, in devices based on exfoliated flakes of two topological semimetals, ZrSiSe and BaMnSb2. Using this method, carrier mobility in ZrSiSe improved by a factor of 3800, resulting in the observation of record-high mobility for exfoliated ZrSiSe. Quantum oscillations in annealed ZrSiSe appeared at magnetic fields as low as 5 T, and magnetoresistance increased by 10,000. We argue that a thermal process underlies this improvement. Finally, Raman spectroscopy and analysis of quantum oscillations in ZrSiSe indicate that the phonon modes and Fermi surface area are unchanged by current annealing. Through current annealing, we had access to suitable device quality, hence could investigate topological semimetals extensively. We studied Shubnikov de Haas oscillations focused on the unexpected frequency of 140 T that is unrelated to any known surface (450 T) or bulk (220 T) Fermi surface. We show that this frequency has a 2D nature by providing angle dependence and thickness dependence of quantum oscillations. Angle dependence of 140 T follows 1/cos(θ), in contrast to bulk frequency, 220 T, which shows no change with angle. In addition, thickness dependence shows that the relative amplitude of 140 T to 220 T exponentially increases by decreasing the thickness. In addition, we provide a comparison of phase analysis of 140 T with 220 T that shows the different origins of these frequencies. We speculate this …
author: Fereidouni Ghaleh Minab, Arash
keywords: 2D semimetal, Fermi arc, Gate effect, Nanotechnology, topological semimetal, Weyl orbit, ZrSi, Condensed Matter Physics, Quantum Physics
date published: 2022-08-01T07:00:00Z
date modified: 2026-07-24T01:00:19Z
provider: University of Arkansas
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Arkansas