Magnetic gap effect on the tunneling conductance in a topological insulator ferromagnet/superconductor junction

The tunneling conductance on the surface of a topological-insulator-based ferromagnet/superconductor (F/S) structure is studied where S is an s-wave superconductor with superconducting order parameter similar to Delta. The conductance is calculated based on the BTK formalism. The magnetization in F is applied along the z-direction ((m) over bar < 0, 0, M >) in order to induce the energy-mass gaps (m) for the Dirac electrons in the F-region. In this work, the influence of energy gap due to the magnetic field in the F-region on the conductance is emphasized. The Fermi energy mismatch between F (E-FF = E-F) and S (E-FS = E-F + U), where the gate potential U is applied to the electrode on top of S. is also considered. As a result, a biased voltage V can cause the conductance switch at eV = Delta, depending on the value of the magnetic field. The conductance is found to be linearly dependent on either m or U. The slope of the curve can also be adjusted. This linear behavior in a topological-insulator-based F/S structure may be valuable for electronic applications of the linear-control-current devices. The tunneling conductances of the quasi-Dirac-particle in a topological-insulator-based F/S junction are quite different from those of a graphene-based F/S junction. (C) 2010 Elsevier B.V. All rights reserved.