Tuning Quantum Transport with Fast Ion Implantation in a Topological Semimetal
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Rha-eunbi993-SM-NSE-2026-thesis.pdf
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12.24 MB
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19d152f3fc0ff33fbce3cb3600c35e04
Author(s)
Rha, Eunbi
Advisor(s)
Li, Mingda
Date Issued
February 2026
Publisher
Massachusetts Institute of Technology
Abstract
The ability to precisely control the electronic and topological properties of quantum materials is central to realizing next-generation quantum technologies. This thesis establishes fast ion implantation as a generalizable methodology for quantum materials engineering, enabling programmable, depth-resolved, and species-selective tuning of material properties. As a case study, cadmium arsenide (Cd₃As₂), a prototypical Dirac semimetal, was modified using niobium ion implantation at controlled energies. Implantation profiles were validated by SRIM/TRIM simulations and secondary ion mass spectrometry, while scanning transmission electron microscopy confirmed that crystalline order was largely preserved despite defect introduction. Electrical transport measurements revealed a pronounced enhancement of negative longitudinal magnetoresistance (NLMR), a signature of the Adler–Bell–Jackiw chiral anomaly: the characteristic minimum shifted from B=4T in pristine films toB=7T in surface-
doped and above B = 9T in bulk-doped films, representing more than a twofold enhancement compared to pristine samples. Density functional theory calculations corroborated that niobium implantation lowers the Fermi level toward the Dirac node, strengthening the anomaly response. These findings contrast with the conventional expectation that disorder suppresses quantum signatures and instead demonstrate that ion implantation can enhance topological transport while maintaining structural integrity. By positioning accelerator-based implantation as a controllable and scalable tuning knob, this work translates topological transport control into a quantum materials engineering strategy for chiraltronic and low-dissipation quantum devices.
MIT Department
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
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