Gate-controlled Supercurrent in Ballistic InSb Nanoflag Josephson\n Junctions

Abstract

High-quality III-V narrow band gap semiconductor materials with strong\nspin-orbit coupling and large Lande g-factor provide a promising platform for\nnext-generation applications in the field of high-speed electronics,\nspintronics, and quantum computing. Indium Antimonide (InSb) offers a narrow\nband gap, high carrier mobility, and a small effective mass, and thus is very\nappealing in this context. In fact, this material has attracted tremendous\nattention in recent years for the implementation of topological superconducting\nstates supporting Majorana zero modes. However, high-quality heteroepitaxial\ntwo-dimensional (2D) InSb layers are very diffcult to realize owing to the\nlarge lattice mismatch with all commonly available semiconductor substrates. An\nalternative pathway is the growth of free-standing single-crystalline 2D InSb\nnanostructures, the so-called nanoflags. Here we demonstrate fabrication of\nballistic Josephson-junction devices based on InSb nanoflags with Ti/Nb\ncontacts that show gate-tunable proximity-induced supercurrent up to 50 nA at\n250 mK and a sizable excess current. The devices show clear signatures of\nsubharmonic gap structures, indicating phase-coherent transport in the junction\nand a high transparency of the interfaces. This places InSb nanoflags in the\nspotlight as a versatile and convenient 2D platform for advanced quantum\ntechnologies.\n