In high-Tc superconductor junctions, due to the sign changing behavior of the pair potential, the zero bias conductance peak (ZBCP) appears in the quasiparticle tunneling spectroscopy. In this paper, we will discuss unresolved problems about ZBCP, i.e., effect of magnetic field and Fermi surface. In the former part of the paper, it is shown that ZBCP does not split into two by the magnetic field, when the transparency of the junction is sufficiently large. In the latter part of the paper, we will extend our theory to include the effect of Fermi surface based on the Green's function theory and linear response theory. We will clarify ZBCP always appears for interface even if we take into account of the Fermi surface mismatch at the interface.
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