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Open Access Publications from the University of California

Scholarly Works (2 results)

  • Thesis
  • Peer Reviewed
UC Santa Barbara Electronic Theses and Dissertations (2024)

This dissertation focuses on the growth and characterization of compounds, devices, and heterostructures with large lattice constant III-V semiconductors (SMs) with high spin orbit coupling. Spin orbit coupling originates from the interaction of the orbital angular momentum and the spin angular momentum of an electron and is a key component in spintronic devices and devices for studying Majorana zero mode physics. The ultraclean environment and precise growth controls of molecular beam epitaxy were used to grow a combination of III-V materials exhibiting high spin-orbit coupling, superconductor-semiconductor devices, and ferromagnet-semiconductor heterostructures.

Rashba spin-orbit interaction is responsible for splitting the degeneracy of spin-up and spin-down electrons. The broken degeneracy is useful for spin generation and detection or creating topological insulator-like devices by applying a magnetic field. Semiconductors exhibiting high spin-orbit coupling can be gated to control both the carrier density and the strength of the Rashba interaction. Here, we use InSb/GaAs (001) to demonstrate a simple and inexpensive heterostructure, which exhibits spin-orbit coupling.

InAs quantum wells (QWs) grown on InP (001) also exhibit large Rashba spin-orbit interaction, but have demonstrated mobilities of µ>1,000,000 cm^2/Vs. In this work, we demonstrate the effects of strain compensation on QW mobility by varying both the strain in the cladding layer and the thickness of the InAs QW. We observe a maximum mobility of µ=1,160,000 cm^2/Vs, which suggests that strain compensation in near surface QWs may improve mobility while enabling proximitized superconductivity.

Until recently, Al was the superconductor of choice for superconductor-semiconductor (SuperSemi) devices. Because of the epitaxial growth mode of Al on InAs and InSb nanowires, the Al/InAs and Al/InSb systems were primarily utilized for SuperSemi devices intended to study Majorana physics. Here we demonstrate that like Al, β-Sn exhibits a hard gap, large critical field, and 2e-charging, which are all requirements for Majorana devices.

Eliciting the Majorana zero mode in a SuperSemi structure currently requires the application of a large, global magnetic field. New proposals have suggested that the large global magnetic field can be replaced with either local micromagnets or ferromagnetic (FM) contacts. However, interfacial reactions between elemental FMs and III-V’s are well known to occur. By using an antimonide-based FM, MnSb, we demonstrate a FM that has tunable magnetic properties and is compatible with III-V heterostructures.

    • Article
    • Peer Reviewed
    LBL Publications (2021)
    Topological materials often exhibit remarkably linear nonsaturating magnetoresistance (LMR), which is both of scientific and technological importance. However, the role of topologically nontrivial states in the emergence of such a behavior has eluded clear demonstration in experiments. Here, by reducing the coupling between the topological surface states (TSS) and the bulk carriers, we controllably tune the LMR behavior in Pt1-xAuxLuSb into distinct plateaus in Hall resistance, which we show arise from a quantum Hall phase. This allowed us to reveal how smearing of the Landau levels, which otherwise gives rise to a quantum Hall phase, results in an LMR behavior due to strong interaction between the TSS with a positive g factor and the bulk carriers. We establish that controlling the coupling strength between the surface and the bulk carriers in topological materials can bring about dramatic changes in their magnetotransport behavior. In addition, our work outlines a strategy to reveal macroscopic physical observables of TSS in compounds with a semimetallic bulk band structure, as is the case in multifunctional Heusler compounds, thereby opening up opportunities for their utilization in hybrid quantum structures.
      Cover page: Identifying the fingerprints of topological states by tuning magnetoresistance in a semimetal: The case of topological half-Heusler Pt1−xAuxLuSb
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