  The 3D topological insulator (TI) PN junction under magnetic fields presents
a novel transport property which is investigated both theoretically and
numerically in this paper. Transport in this device can be tuned by the axial
magnetic field. Specifically, the scattering coefficients between incoming and
outgoing modes oscillate with axial magnetic flux at the harmonic form. In the
condition of horizontal mirror symmetry, the initial phase of the harmonic
oscillation is dependent on the parities of incoming and outgoing modes. This
symmetry is broken when a vertical bias is applied which leads to a kinetic
phase shift added to the initial phase. On the other hand, the amplitude of
oscillation is suppressed by the surface disorder while it has no influence on
the phase of oscillation. Furthermore, with the help of the vertical bias, a
special (1,-2) 3D TI PN junction can be achieved, leading to a novel spin
precession phenomenon.
