Clean electrostatically defined constrictions in strontium titanate.

Electrostatic control of ballistic constrictions in SrTiO₃ will be presented. Clean nanoscale patterns were defined by combining global carrier accumulation by an ionic liquid with selective local screening by dielectric gates. An order of magnitude improvement in cleanliness metrics was accomplished by inserting a HfO_x barrier layer between the ionic liquid dipoles and the patterned 2D electron gas accumulated in SrTiO₃. Clear conductance quantization characteristic of a clean quantum point contact was observed. The ballistic subbands displayed a surprising tendency to retain spin degeneracy up to very high magnetic fields, a likely signature of pairing interactions acting even in the absence of a globally coherent superconducting order.