Tunable coupling of two-dimensional superconductors in bilayer SrTiO ₃ heterostructures

Interlayer coupling effects between high mobility two-dimensional superconductors are studied in bilayer δ-doped SrTiO₃ heterostructures. By tuning the undoped SrTiO₃ spacer layer between the dopant planes, clear tunable coupling is demonstrated in the variation of the sheet carrier density, Hall mobility, superconducting transition temperature, and the temperature and angle dependencies of the superconducting upper critical field. Systematic variation is found between one effective (merged) two-dimensional superconductor to two decoupled two-dimensional superconductors. In the intermediate coupled regime, a crossover is observed due to coupling arising from intersubband interactions.