Long correlated paths

Phys. Rev. Lett. 117, 096801 (2016)

Lithographic processes based on conductive atomic force microscopy have been exploited recently to generate ultranarrow, quasi-one-dimensional conductive regions with outstanding transport properties at the interface of two oxide materials. This approach provides a novel platform to explore the effects of the reduced dimensionality on a variety of correlated electronic ground states emerging in complex oxide heterostructures. In particular, nanowires patterned on the LaAlO₃/SrTiO₃ interface have led to the unexpected observation of robust electron pairing without evidence for superconductivity.

Now, Jeremy Levy and colleagues at the University of Pittsburgh and the University of Wisconsin-Madison in the US have demonstrated the ballistic transport of electron pairs over micrometre distances. The researchers used conductive atomic force microscope lithography on LaAlO₃/SrTiO₃ interfaces to pattern nanowires up to 4 μm in length that are delimited by semitransparent barriers and act as optical cavities. They studied the differential conductance maps of these regions at ultralow temperatures as a function of the external magnetic field and of both source–drain and side-gate voltages. This revealed clear oscillations arising from quantum interference processes. Although appearing at magnetic field values much higher than the upper critical field for superconductivity, these oscillations were synchronous with those arising in the superconducting phase, suggesting an intimate relation between the superconducting and paired regimes. These observations confirm the ballistic nature of transport within a correlated state — a limit unexplored to date.