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Quantum transport in mesoscopic systems of Bi and other strongly spin-orbit coupled materials
|dc.description.abstract||Systems with strong spin-orbit coupling are of particular interest in solid state physics as|
an avenue for observing and manipulating spin physics using standard electrical techniques.
This dissertation focuses on the characteristics of elemental bismuth (Bi), which exhibits
some of the strongest intrinsic spin-orbit coupling of all elements, and InSb, which exhibits
some of the strongest intrinsic spin-orbit coupling of all compound semiconductors. The
experiments performed study the quantum transport signatures of nano- and micron-scale
lithographically defined devices as well as spin-orbit coupled material/ferromagnet interfaces.
All Bi structures are fabricated from Bi thin "films, and hence a detailed analysis of
the characteristics of Bi "film growth by thermal evaporation is provided. Morphologically
and electrically high quality "films are grown using a two stage deposition procedure. The
phase and spin coherence of Bi geometries constrained in one, two, and three dimensions
are systematically studied by analysis of the weak antilocalization transport signature, a
quantum interference phenomenon sensitive to spin-orbit coupling. The "findings indicate
that the phase coherence scales proportionally to the limiting dimension of the structure
for sizes less than 500 nm. Specifically, in Bi wires, the phase coherence length is approximately as long as the wire width. Dephasing due to quantum confinement e"ffects limit the phase coherence in small Bi structures, impairing the observation of controlled interference phenomena in nano-scale Bi rings. The spin coherence length is independent of dimensional constraint by the film thickness, but increases significantly as the lateral dimensions, such as wire width, are constrained. This is a consequence of the quantum transport contribution from the strongly spin-orbit coupled Bi(001) surface state. To probe the Bi surface state further, Bi/CoFe junctions are fabricated. The anisotropic magnetoresistance of the CoFe is modifi"ed when carriers tunnel into the CoFe from Bi, possibly due to a spin dependent tunneling process or an interaction between the spin polarized density of states in CoFe and the anisotropic spin-orbit coupled density of states in Bi. InSb/CoFe junctions are studied as InSb "films are a simpler spin-orbit coupled system compared to Bi "films. For temperatures below 3.5 K, a large, symmetric, and abrupt negative magnetoresistance is observed. The low-"field high resistance state has similar temperature and magnetic "field dependences as the superconducting phase, but a superconducting component in the device measurements seems absent. A differential conductance measurement of the InSb/CoFe interface during spin injection indicates a quasiparticle gap present at the Fermi energy, coinciding with the large magnetoresistance.
|dc.title||Quantum transport in mesoscopic systems of Bi and other strongly spin-orbit coupled materials||en_US|
|thesis.degree.grantor||Virginia Polytechnic Institute and State University||en_US|
|dc.contributor.committeechair||Heremans, Jean Joseph||en_US|
|dc.contributor.committeemember||Soghomonian, Victoria Garabed||en_US|
|dc.contributor.committeemember||Link, Jonathan Marion||en_US|
|dc.contributor.committeemember||Scarola, Vito W.||en_US|
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Doctoral Dissertations