Thursday, November 10, 2016 - 3:30pm
Mengchen Huang, Department of Physics, UCSB
Complex oxide heterointerfaces exhibit rich physics as well as many veiled puzzles. LaAlO3/SrTiO3 (LAO/STO) is one of the prototype of such heterointerfaces. Emergent phenomena like metal-insulator transition, piezoresponse, superconductivity, magnetism, strong spin-orbit coupling and coexistence of superconductivity and magnetism were reported in LAO/STO. However, the origin of the conducting interface is still the subject of intense debate, and the physics behind these emergent phenomena remains a wild space to be explored. Local probe— nanostructures created by conductive atomic force microscope (c-AFM) lithography and the AFM itself can be a powerful tool to investigate these novel phenomena at nanoscale dimensions. After introducing the LAO/STO heterostructure and c-AFM lithography technique, the presentation will focus on using piezoresponse force microscope (PFM) to study the electromechanical response and using magnetic force microscope (MFM) to search room temperature magnetism at LAO/STO interface. The PFM results indicate that the carrier density mediates lattice distortions at the interface, and surface adsorbates can affect the PFM signal via coupling to the interfacial electrons. The developed high-resolution, non-destructive PFM imaging technique visualizes nanostructures at LAO/STO interface. In the MFM study, an in-plane ferromagnetic phase emerges as electrons are depleted from the interface and vanishes as the interface is modulated to be conducting via electrical top gating. Repeated cycling of the gate voltage results in new, uncorrelated magnetic patterns.
October 13, 2016 - 4:37pm