  The hysteretic piezoelectric response in LaAlO3/SrTiO3 heterostructures can
provide important insights into the mechanism for interfacial conductance and
its metastability under various conditions. We have performed a variety of
nonlocal piezoelectric force microscopy experiments on 3 unit cell
LaAlO3/SrTiO3 heterostructures. A hysteretic piezoresponse is observed under
various environmental and driving conditions. The hysteresis is suppressed when
either the sample is placed in vacuum or the interface is electrically
grounded. We present a simple physical model which can account for the observed
phenomena.
