| Summary: | 碩士 === 國立臺灣師範大學 === 物理學系 === 96 === This thesis applies the theory of tunneling to study different kinds of metal/insulator/ superconductor (N/I/S) junctions. Chapter 1 gives a brief review of the BCS theory. Chapter 2 mentions some basic properties of high-temperature superconductors (HTSC). Possible coexistence of antiferromagnetic (AF) order and the superconducting order in HTSC is emphasized. In chapter 3, theories of tunneling are presented, namely the Blonder-Tinkham-Klapwijk model approach and the tunneling Hamiltonian approach. In chapter 4, we summarize recent experimental and theoretical works on different kinds of N/I/S junctions. Chapter~5 is based on one of my recent paper to be published. We extend the theory of point-contact spectroscopy [Phys. Rev. B 76, 220504(R) (2007). This paper argued that the splitting of zero-bias conductance peak (ZBCP) in electron-doped cuprate superconductor point-contact spectroscopy is due to the coexistence of AF and $d$-wave superconducting orders.]
to study the ferromagnetic metal/electron-doped cuprate
superconductor (FM/EDSC) junctions. In addition to the AF order, effects of spin polarization, Fermi-wave vector mismatch (FWM) between the FM and EDSC regions, and effective barrier are also considered. They play a crucial role in determining the spin polarization value. It is shown that there exits the midgap surface state (MSS) contribution to the ZBCP in the junction and Andreev
reflections are largely modified due to the exchange field of ferromagnetic metal. A more accurate formula is proposed for determining the spin polarization value in combination with the conductance in point-contact experimental data. Finally in Chapter~6, a brief conclusion and future prospects are given.
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