In-situ growth and fabrication of planar ferromagnetic semiconductor-based Josephson junctions*

The superconductor(S)/ferromagnet(F)/superconductor(S) structures attract attention as a platform of unconventional superconductivity. For the realization of practical SFS devices and novel emergent states such as Majorana fermions, improvement of the S/F interface quality is required. We report an in-situ epitaxial growth using molecular beam epitaxy (MBE) and fabrication of nano-size Josephson junctions (JJs) with s-wave superconductor Al electrodes grown on (In,Fe)As or InAs/(Ga,Fe)Sb heterostructures, where (In,Fe)As and (Ga,Fe)Sb are Fe-doped FMSs. The InAs junctions are made ferromagnetic either by doping Fe [(In,Fe)As] or by the magnetic proximity effect from an Fe-doped FMS [(Ga,Fe)Sb] [1]. We fabricate planar Al/FMS/Al JJ structures with a nano-size trench (< 100 nm) by electron beam lithography. Electrical transport measurements confirmed that the Al layers are superconducting with critical temperature T_C of 1 – 1.2 K. In the presentation, we will further discuss many aspects of epitaxial growth and electrical transport measurements in these ferromagnetic JJs.
[1] K. Takiguchi et al., Nat. Phys. 15, 1134 (2019).