Superconducting split-gate quantum point contacts in ionic liquid-gated SrTiO₃

SrTiO₃ is one of few materials to exhibit superconductivity at carrier densities low enough to be manipulated electrostatically. In this work, we demonstrate electrostatically defined superconducting devices that combine global ionic liquid gating of the leads with local dielectric split gates. This design enables patterning of a 2D electron system with sub-100 nm features without the need for mesa etching.
When tuned into a normal state, these devices behave as ballistic quantum point contacts, with conductance quantization near pinch-off. Quantization is in increments of e²/h, even at zero magnetic field, suggesting spontaneous spin-polarization.
When the device leads are tuned to be superconducting, the weak link can be gated through a sequence of transport regimes: pinch-off, coulomb blockade, superconducting tunnel junction, and SNS or SS’S Josephson junction. We demonstrate that the local constriction can be tuned into a regime where its critical field exceeds that of its superconducting leads. This offers promise of exploring the microscopic physics of underdoped SrTiO₃, where two-dimensional superconductivity is usually suppressed by the lack of macroscopic coherence.