Special Colloquium: Harold Y. Hwang

Title: Probing 2D Crystallinity and Superconductivity in Oxide Heterostructures

Speaker: Harold Y. Hwang

            Departments of Applied Physics and Photon Science, 

                Stanford University and SLAC National Accelerator Laboratory

Place：Room 201, Building 12, Yuquan Campus

Time：Nov. 19th, Monday, 10:00-11:00

Abstract

Long-range order and phase transitions in two-dimensional (2D) systems have been important research topics for decades, with much current interest due to new materials systems for their investigation. Here we use oxide heterostructures to explore aspects of 2D crystalline order and superconductivity. For the first topic, we study ultrathin membranes of SrTiO₃, an archetypal perovskite oxide with isotropic (3D) bonding. Atomically controlled membranes are released by dissolving an underlying epitaxial layer. Although all unreleased films are initially single-crystalline, the SrTiO₃lattice collapses below a critical thickness (5 unit cells). This crossover from algebraic to exponential decay of the crystalline coherence length reflects the Berezinskii-Kosterlitz-Thouless (BKT) transition, which has the unusual feature here of being driven by chemical bond breaking at the 2D layer – 3D bulk interface. For the second topic, we use dual electrostatic gatesto independently control the carrier density and disorder of the 2D superconductor at the LaAlO₃/SrTiO₃interface, enabling a comprehensively map of the phase diagram. We observe a sequence of transitions from an insulator, ‘metal’, through a pseudo-gap phase corresponding to precursor pairing, and finally the establishment of long-range phase coherence.

About the Speaker

Harold Y. Hwang is a Professor of Applied Physics and Photon Science (SLAC) at Stanford University. He received a B.S. in Physics, B.S. and M.S. in Electrical Engineering from MIT (1993), and a Ph.D. in Physics from Princeton University (1997). He was formerly a Member of Technical Staff at Bell Labs (1996-2003), Associate Professor and Professor at the University of Tokyo (2003-2010). His current research focuses on atomic-scale synthesis of heterostructures of quantum materials; control of the electronic structure at interfaces and in confined geometries; low-dimensional superconductivity; and novel devices based on interface and surface states in oxides. Recognitions include the MRS Outstanding Young Investigator Award (2005), the IBM Japan Science Prize (Physics, 2008), Fellowship in the American Physical Society (2011), the Ho-Am Prize (Science, 2013), and the Europhysics Prize (2014, with Jochen Mannhart and Jean-Marc Triscone).

Welcome to attend!