Vortex Critical State in an Oxide Superconductor 

Superconductors in two-dimensions (2D) have been shown to exhibit unique effects such as Berezinskii–Kosterlitz–Thouless transition and Pauli-limit violation. In the 2D limit the effect of the screening of magnetic fields can be neglected and a critical state of vortices can be realised. This has been predicted to introduce a non-trivial dependence of the critical current on the magnetic field, allowing for extraction of characteristic properties of the superconducting state. Here we present measurements of this critical state realised in a heterostructure based on the complex oxide KTaO₃. Regimes dominated by surface and bulk pinning of vortices are identified. Beyond a characteristic field we are able to observe switching to a vortex-induced dissipative state preceding the transition to the normal state. This dissipative state displays unusual I-V characteristics and switching behaviour. These results establish KTaO₃ as a platform to study the rich phenomena of vortex matter in 2D.