Superconducting, insulating and anomalous metallic regimes in a gated two-dimensional semiconductor–superconductor array

The superconductor–insulator transition in two dimensions has been widely investigated as a paradigmatic quantum phase transition. The topic remains controversial because many experiments exhibit a metallic regime with saturating low-temperature resistance, which is at odds with conventional theory. Here, we explore this transition in a highly controllable system, a semiconductor heterostructure with epitaxial aluminium, patterned to form a regular array of superconducting islands connected by a gateable quantum well. Spanning nine orders of magnitude in resistance, the system exhibits regimes of superconducting, metallic and insulating behaviour, along with signatures of flux commensurability and vortex penetration. An in-plane magnetic field eliminates the metallic regime, restoring the direct superconductor–insulator transition; it also improves the scaling behaviour while strongly altering the scaling exponent.The phase transition between a superconductor and insulator is examined in a new type of heterostructure. A metallic regime is found, which disappears in a magnetic field, giving fresh insight to a paradigmatic quantum phase transition.