Jing XuFollow

Publication Date

2019

Document Type

Dissertation/Thesis

First Advisor

Xiao, Zhili

Degree Name

Ph.D. (Doctor of Philosophy)

Legacy Department

Department of Physics

Abstract

Magnetic field induced resistance change is conventionally termed as magnetoresistance (MR), which is usually related to magnetism and plays crucial roles in applications such as sensors and storage devices. In a single-band nonmagnetic material, the semiclassical Boltzmann equation approach gives rise to a magnetic field independent resistivity. With the recent discovery of topological materials, extremely large magnetoresistance (XMR) and negative longitudinal magnetoresistance (NLMR) have been observed in a variety of materials. In this dissertation I investigated XMRs in the rare-earth monopnictides (LaSb and YSb), which are non-saturating with increasing magnetic field, accompanying with a turn-on temperature behavior of the magnetoresistivity. I also observed a saturating XMR behavior as well as a reentrant metallic behavior of the magnetoresistivity at low temperatures in a Weyl semimetal (NbP) of Group V transition-metal monophosphides. My results reveal that the XMR behavior originates from ultrahigh mobility of the charge carriers and nearly perfect compensation of the electron and hole density. This research shows that Hall factor (����) is the experimental parameter to reveal the important role played by Hall Effect in the XMR phenomenon.

This dissertation research also uncovers a negative longitudinal MR behavior in gallium arsenide quantum wells. Microscopic disorder that causes current path distortion in the high-quality quantum wells is proposed to be the origin of the observed NLMRs. A phenomenological three-resistor model is developed to describe the various magnetoresistance behaviors observed in experiments. The results provide an alternative mechanism to explain NLMRs in other materials such as topological single crystals, in which the NLMRs are considered to be associated with Weyl fermions that have a defined chirality.

Extent

110 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

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