Magnetotransport measurements are used to probe materials of interest to study exotic phases of matter
The bulk of my research in magnetotransport measurements was during the summer and fall of 2017 as an undergraduate research fellow in Dr. Kenneth Burch's LASE lab.
Magnetotransport measurements electrically probe samples in magnetic fields in order to study the fundamental physical properties of the charge carriers within the samples. Exotic states of matter are interesting in their own right, but can also be utilized in novel technologies and devices. For example, Majorana fermions may be used for robust quantum computation in which information is not sensitive to the local perturbations which are a notable hindrance to contemporary quantum computing efforts.
More information can be found in each of the below sections.
During this project, I was working under the mentorship of Mason J. Gray [website] [orcid], a LASE graduate researcher at the time, to assist him in his studies into topological insulator/superconductor heterojunctions.
A motivation for these studies was to study the nature of the superconductivity of the material Iron Telluride Selenide (FTS). In particular, ordinary superconductivity occurs when electrons form "Cooper pairs", bound together by phonon exchange. If the electrons are bound together by anything other than phonon exchange, e.g. spin fluctuations, then the superconductivity is called unconventional . My responsibilities included fabricating and measuring heterojunctions composed of the superconductor FTS and the topological insulators Bismuth Selenide (BS) and Bismuth Telluride (BT) to aid Mason's studies into the nature of the physical effects which occur at the interfaces between these materials.
The materials of interest for these studies are composed of layers of atoms. Within the layers, atoms are held together by strong interatomic forces, but the layers themselves are held together by weak Van der Waals forces. This makes the materials easy to cleave, leaving pristine interfaces that can be juxtaposed to study interface effects.
This fabrication process is exactly what I did to create the heterojunctions for this study. The fabrication took place in LASE argon glovebox (pictured below) to prevent oxidation and contamination.
After juxtaposing the materials of interest, I wired them with silver paint to sample holders, and inserted them into LASE's 9T magnet.
Once in LASE's magnet, I performed magnetotransport measurements by measuring the differential conductance of the sample between different points as a function of magnetic field strength and angle.
Below we see how the differential conductance of the sample is attenuated as the magnitude of a magnetic field coplanar with the device interface increases.
I gave a presentation as part of the NSF REU program which funded this research. The presentation can be found here.
Related publication: Evidence for Helical Hinge Zero Modes in an Fe-Based Superconductor (link)
 Unconventional Superconductivity, G.R. Stewart. AIP Vol 66, Issue 2. (2017)