Carrier density and disorder tuned superconductor-metal transition in a two-dimensional electron system

Quantum ground states that arise at atomically controlled oxide interfaces provide an opportunity to address key questions in condensed matter physics, including the nature of two-dimensional metallic behaviour often observed adjacent to superconductivity. At the superconducting LaAlO 3 /SrTiO 3 interface, a metallic ground state emerges upon the collapse of superconductivity with field-effect gating and is accompanied with a pseudogap. Here we utilize independent control of carrier density and disorder of the interfacial superconductor using dual electrostatic gates, which enables the comprehensive examination of the electronic phase diagram approaching zero temperature. We find that the pseudogap corresponds to precursor pairing, and the onset of long-range phase coherence forms a two-dimensional superconducting dome as a function of the dual-gate voltages. The gate-tuned superconductor–metal transitions are driven by macroscopic phase fluctuations of Josephson coupled superconducting puddles. Studying quantum phase transitions at oxide interfaces provide a key to understand emergent two-dimensional (2D) superconductivity. Here, Chen et al. report comprehensive electronic phase diagram of the 2D electron system at the superconducting LaAlO 3 /SrTiO 3 interface with independent control of carrier density and disorder.