Event
Ph.D. Dissertation Defense: Brendan Jordan
Thursday, June 11, 2026
10:00 a.m.
AVW 2460
Emily Irwin
301 405 0680
eirwin@umd.edu
ANNOUNCEMENT: Ph.D. Dissertation Defense
Name: Brendan Jordan
Committee:
Professor Kevin Daniels (Chair)
Professor Neil Goldsman
Professor Cheng Gong
Initial research confirmed the presence of low temperature surface states, and subsequent studies have provided additional evidence of topological states, such as spin-momentum locking in transport measurements. Additionally, a bulk Fermi surface has been measured by de Haas van Alphen oscillations, raising further questions about the robustness of the bulk insulating state. Intrinsic explanations have been brought forward, as well as evidence for extrinsic causes, such as impurity atoms and vacancies that may break the hybridization between f-orbital and conduction electrons resulting in local conducting states. Further testing is needed to understand the effects of different sources of disorder on the Kondo gap. Measurements have also been done to test the performance of SmB6 in spintronic applications, where the materials have been shown to produce charge currents from magnetic polarization via the inverse Edelstein effect, and thin films have demonstrated potential for use in spin-orbit torque devices.
Most research has been done on bulk crystals grown through Al-based flux or float zone methods. Thin films of 50-500nm have also been grown using magnetron sputtering and pulsed laser deposition. Recently, CVD-grown nanostructures were synthesized, consisting of single crystal rectangular rods roughly a few hundred nanometers thick. These methods have issues with scalability, crystallinity, and defects, which affect key material metrics as well as device performance
This research focuses on the scalable synthesis of thin film SmB6 on metal-catalyzed silicon by chemical vapor deposition (CVD) and the fabrication of spintronic devices. The performance of fabricated devices should improve with better material crystallinity and larger grain sizes. CVD enables better control of crystal quality, removes additional sources of local disorder, and allows for scalable synthesis and device fabrication that is limited in conventional bulk and nanocrystalline growth methods.
X-ray diffraction (XRD) and Raman of our synthesized thin film SmB6 suggest better crystallinity compared to sputtered thin films, with a strong preference for growth in the (100) direction. However, surface roughness and uniformity remain issues, with film thicknesses varying from 1-3μm. Resistivity measurements show a low temperature-to-high temperature ratio of ~70 in the middle of reported bulk and nanostructured/sputtered samples. Magnetoresistance measurements also show linear behavior at 3K, suggesting surface transport. An electrochemical etching process is developed to aid in processing films.
Committee:
Professor Kevin Daniels (Chair)
Professor Neil Goldsman
Professor Cheng Gong
Professor Thomas Murphy
Professor John Cumings (Dean's Representative)
Date/Time: Thursday, June 11, 2026, 10:00 am
Location: AVW 2460
Title: Growth of Samarium Hexaboride by Chemical Vapor Deposition
Professor John Cumings (Dean's Representative)
Date/Time: Thursday, June 11, 2026, 10:00 am
Location: AVW 2460
Title: Growth of Samarium Hexaboride by Chemical Vapor Deposition
Abstract:
Samarium hexaboride (SmB6) has attracted significant interest over the past decade as a predicted Kondo topological insulator, the first of its kind. Topological insulators have already been shown as promising candidates in spintronics. However, unlike conventional topological insulators, which can suffer from impurity-induced in-gap states, the energy gap in SmB6 arises from strong electron interactions, specifically hybridization of local f-orbital and conduction electrons, as a Kondo insulator. The energy gap in SmB6 (~20meV) may be more robust and improve certain bulk resistance limitations found in other topological insulators. Verification of the topological nature, however, has proven difficult due to issues involving polarized surfaces and the small Kondo gap of only ~20meV that is difficult to resolve by most ARPES measurements.
Initial research confirmed the presence of low temperature surface states, and subsequent studies have provided additional evidence of topological states, such as spin-momentum locking in transport measurements. Additionally, a bulk Fermi surface has been measured by de Haas van Alphen oscillations, raising further questions about the robustness of the bulk insulating state. Intrinsic explanations have been brought forward, as well as evidence for extrinsic causes, such as impurity atoms and vacancies that may break the hybridization between f-orbital and conduction electrons resulting in local conducting states. Further testing is needed to understand the effects of different sources of disorder on the Kondo gap. Measurements have also been done to test the performance of SmB6 in spintronic applications, where the materials have been shown to produce charge currents from magnetic polarization via the inverse Edelstein effect, and thin films have demonstrated potential for use in spin-orbit torque devices.
Most research has been done on bulk crystals grown through Al-based flux or float zone methods. Thin films of 50-500nm have also been grown using magnetron sputtering and pulsed laser deposition. Recently, CVD-grown nanostructures were synthesized, consisting of single crystal rectangular rods roughly a few hundred nanometers thick. These methods have issues with scalability, crystallinity, and defects, which affect key material metrics as well as device performance
This research focuses on the scalable synthesis of thin film SmB6 on metal-catalyzed silicon by chemical vapor deposition (CVD) and the fabrication of spintronic devices. The performance of fabricated devices should improve with better material crystallinity and larger grain sizes. CVD enables better control of crystal quality, removes additional sources of local disorder, and allows for scalable synthesis and device fabrication that is limited in conventional bulk and nanocrystalline growth methods.
X-ray diffraction (XRD) and Raman of our synthesized thin film SmB6 suggest better crystallinity compared to sputtered thin films, with a strong preference for growth in the (100) direction. However, surface roughness and uniformity remain issues, with film thicknesses varying from 1-3μm. Resistivity measurements show a low temperature-to-high temperature ratio of ~70 in the middle of reported bulk and nanostructured/sputtered samples. Magnetoresistance measurements also show linear behavior at 3K, suggesting surface transport. An electrochemical etching process is developed to aid in processing films.
