THz- and infrared ellipsometry studies of plasmonic modes in complex oxide heterostructures

I will present THz- and infrared ellipsometry studies of complex oxide heterostructures with mobile charge carriers that are spatially confined. The first example concerns the two-dimensional electron gas in LaAlO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3}}$ and related materials for which the sheet carrier density, the depth profile and the mobility of the charge carriers are obtained from the analysis of a so-called Berreman-mode. The second example is about Pr$_{\mathrm{0.5}}$La$_{\mathrm{0.2}}$Ca$_{\mathrm{0.3}}$MnO$_{\mathrm{3}}$/YBa$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{7}}$/Pr$_{\mathrm{0.5}}$La$_{\mathrm{0.2}}$Ca$_{\mathrm{0.3}}$MnO$_{\mathrm{3}}$ (PYP) trilayers for which we recently discovered a very unusual kind of insulator-to-superconductor transition as a function of an applied magnetic field. Our THz-ellipsometry and magneto-transport data reveal that the insulator-like response at zero magnetic field arises in fact from a granular superconducting state with very efficient domain boundaries that completely block the superconducting phase coherence.