题目: Probing 2D Crystallinity and Superconductivity in OxideHeterostructures

报告人: Harold Y. Hwang

          Departmentsof Applied Physics and Photon Science,

              StanfordUniversity and SLAC National Accelerator Laboratory

地点：教十二-201

时间：11月19日，周一，10:00-11:00

Abstract

Long-range order and phase transitions in two-dimensional (2D) systemshave been important research topics for decades, with much current interest dueto new materials systems for their investigation. Here we use oxideheterostructures to explore aspects of 2D crystalline order andsuperconductivity. For the first topic, we study ultrathin membranes of SrTiO₃,an archetypal perovskite oxide with isotropic (3D) bonding. Atomicallycontrolled membranes are released by dissolving an underlying epitaxial layer.Although all unreleased films are initially single-crystalline, the SrTiO₃latticecollapses below a critical thickness (5 unit cells). This crossover fromalgebraic to exponential decay of the crystalline coherence length reflects theBerezinskii-Kosterlitz-Thouless (BKT) transition, which has the unusual featurehere of being driven by chemical bond breaking at the 2D layer � 3D bulkinterface. For the second topic, we use dual electrostatic gatestoindependently control the carrier density and disorder of the 2D superconductorat the LaAlO₃/SrTiO₃interface, enabling a comprehensivelymap of the phase diagram. We observe a sequence of transitions from aninsulator, ‘metal’, through a pseudo-gap phase corresponding to precursorpairing, 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. inElectrical Engineering from MIT (1993), and a Ph.D. in Physics from PrincetonUniversity (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 ofheterostructures of quantum materials; control of the electronic structure atinterfaces and in confined geometries; low-dimensional superconductivity; andnovel devices based on interface and surface states in oxides. Recognitionsinclude the MRS Outstanding Young Investigator Award (2005), the IBM JapanScience Prize (Physics, 2008), Fellowship in the American Physical Society(2011), the Ho-Am Prize (Science, 2013), and the Europhysics Prize (2014, withJochen Mannhart and Jean-Marc Triscone).

Welcome to attend!