Phase separation in BaPb1-xBixO3 and fermiology of hole-doped PbTe : insights to understand superconductivity in valence-disproportionated systems
- Valence disproportionated materials are an intriguing class of compounds in which ions of the same chemical element exist in two different states of oxidation. In this thesis, I have studied two anomalous superconductors that are based on materials that exhibit charge disproportionation. My experiments, which probe details of the crystal structure (via high resolution transmission electron microscopy) and of the electronic structure (via quantum oscillations), reveal key aspects of both systems that are associated with the superconductivity. In the case of the first system, the bismuthate BaPb1-xBixO3, we reveal a stripe-like nano-scale structural phase separation for superconducting compositions. This phase separation appears to be a key component in shaping the superconducting dome in this material, leading to a crossover from an inhomogeneous macroscopic superconductor to a granular superconductor for which phase fluctuations suppress Tc. Significantly, this observation implies that this material is intrinsically a higher temperature superconductor. The second family of materials studied in this PhD thesis is one resulting from hole doping in the narrow band gap semiconductor PbTe. The only impurity known to produce superconductivity in this host material is Tl, which has previously been tentatively associated with dynamic valence fluctuations of the Tl impurities. We performed a full Fermi surface characterization of Pb1-xTlxTe, as well as its non-superconducting analog, Pb1-xNaxTe, via Shubnikov de Haas oscillations in magnetotransport, for fields up to 35T (DC). Our results indicate the presence of incoherent resonant impurity levels for Tl concentrations beyond a critical value. The presence or absence of these states at or near the Fermi energy is intimately connected to the presence or absence of superconductivity in doped PbTe. We also show that the Fermi surface of these compounds, in the low temperature regime and for carriers concentrations up to 1x10^20cm^−3, is in fact simpler than has been previously thought, deriving from a single-non-parabolic band.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Giraldo Gallo, Paula
|Stanford University, Department of Physics.
|Statement of responsibility
|Paula Giraldo Gallo.
|Submitted to the Department of Physics.
|Thesis (Ph.D.)--Stanford University, 2015.
- © 2015 by Paula Liliana Giraldo Gallo
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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