Influence of gated-potential and magnetization on the transport of Dirac fermions on topological insulators

Abstract

We theoretically study the transport properties of Dirac fermions in normal metal (N)/ferromagnetic insulator (FI)/superconductor (S) junctions, as well as in N/FI/N junctions, both formed on the surface of a three-dimensional strong topological insulator. In these systems, a ferromagnetic strip provides a Zeeman field m over a region of width $d_0$. We focus on the tuning of the combination of magnetization and gate-tuned potential in the FI and show that the conductance behavior of both junctions exhibits rich features: in the N/FI/N junction, a magneto-electric switch occurs depending on the gate voltage $V_0$ with the pre-loaded magnetization; in the N/FI/S junction, we demonstrate that the role of the gate-tuned potential $V_0$ is similar to that of a Zeeman field m, with its orientation dependent on the superconducting pairing potentials, which reveals that Majorana zero-energy modes can be achieved without magnetization under appropriate Fermi surface mismatch. Our results show that the gate-tuned Fermi energy significantly impacts the transport properties of quantum junctions on the surface of a strong three-dimensional topological insulator, providing valuable guidance for exploring novel directions in transport phenomena that can be verified in realistic experimental setups.