Speaker
Description
It was shown in 2004 that a two-dimensional electron gas may form at the interface between non-polar SrTiO$_3$ and polar cap layers such as LaAlO$_3$. Ongoing interest in these interfaces is sustained by observations of gate-tunable superconductivity, ferromagnetism, and spin-orbit and polaronic effects. This talk will focus on the interfacial electronic structure, which is not well understood even a decade later.
In particular, I will show that the electron distribution at the interface is fundamentally tied to a nearby ferroelectric quantum critical point: energetically, the SrTiO$_3$ lattice favours a ferroelectric transition which, however, is suppressed by quantum fluctuations. Consequently, the SrTiO$_3$ dielectric susceptibility is a strong function of temperature, electric field, and wavevector. As this dielectric susceptibility shapes the confining potential well at the interface, one must expect the electron distribution to also be a strong function of temperature and gate voltage. One of the most striking manifestations of quantum criticality is the prediction that the electron gas becomes deconfined from the interface at low temperatures and densities, opposite to what would be found in conventional semiconductor interfaces.
