Signatures of tunable Majorana-fermion edge states

Chiral Majorana-fermion modes are shown to emerge as edge excitations in a superconductor-topological-insulator hybrid structure that is subject to a magnetic field. The velocity of this mode is tunable by changing the magneticfield magnitude and/or the superconductor`s chemical potential. We discuss how quantum-transport measurements can yield experimental signatures of these modes. A normal lead coupled to the Majorana-fermion edge state through electron tunneling induces resonant Andreev reflections from the lead to the grounded superconductor, resulting in a distinctive pattern of differential conductance peaks.