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Dissertation
Point contact tunneling study of the high transition temperature superconductor Bi₂Sr₂CaCu₂O₈
Doctor of Philosophy (Ph.D.), Drexel University
1991
DOI:
https://doi.org/10.17918/00009716
Abstract
The point-contact (Pt-Ir probe) tunneling measurements on high-T_c superconducting Bi₂Sr₂CaCu₂O₈ single crystals (T_c = 82 K) have been performed at low temperatures of 4.2 K to 77 K. A high conductance region around the origin, which is attributed to the junction of the pure-metallic-bridge type of point-contact tunneling, has been observed. There are also several current steps beyond the high conductance region in the I-V curves, corresponding to conductance troughs, which are either zero or negative, in the dI/dV characteristics in the tunneling spectra. These are pronounced structures indicative of bound states in tunneling spectroscopy. A superconducting energy gap of [Delta] = 28 ± 2 meV has been identified from tunneling spectra taken at T = 4.2 K and as a function of temperature. Current jumps and drops with some regularity in voltage intervals between jumps occur at high applied voltage (>100 mV). This resonance tunneling is the result of the effects of quantization due to the layered-structure of the crystal. A model based on the superlattice-like nature of the crystal has been developed to interpret the tunneling observation of the bound states and the energy gap. Based upon such a model and experimental data, the energy levels of the bound states have been estimated to be "n[epsilon]₀" with n an integer and energy spacing [epsilon]₀ = 8.3 ± 0.3 meV. The Fermi velocity of quasiparticles in the Bi₂Sr₂CaCu₂O₈ single crystal can be calculated from the energy spacing [epsilon]₀ and lattice constant of the crystal, and the value of v_F [approx equals] 1.2x10⁶ cm·sec⁻¹ has been obtained. Hence the coherence length [xi] has been evaluated to be around 0.9 Å using this value of the Fermi velocity. The values of the superconducting energy gap, [Delta], the Fermi velocity, v_F, and the coherence length, [xi], obtained in the present work, are in good agreement with the results reported in the literature. The modeling and the results reported here are original.
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Details
- Title
- Point contact tunneling study of the high transition temperature superconductor Bi₂Sr₂CaCu₂O₈
- Creators
- Mian Heng Jiang
- Contributors
- Allen Rothwarf (Advisor) - Drexel University, Drexel University (1970-)Kevin J. Scoles (Advisor) - Drexel University, Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xi, 148 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- College of Engineering (1970-2026); Drexel University
- Other Identifier
- 991021888793504721