Surface reconstructions and modified surface states in $\mathrm{L}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{a}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$

Surface reconstructions and modified surface states in $L a_{1 - x} C a_{x} Mn O_{3}$

Rama K. Vasudevan, Hemant Dixit, Alexander Tselev, Liang Qiao, Tricia L. Meyer, Valentino R. Cooper, Arthur P. Baddorf, Ho Nyung Lee, P. Ganesh, and Sergei V. Kalinin

Phys. Rev. Materials 2, 104418 – Published 31 October 2018

Abstract

The unique functionalities present at surfaces and interfaces of complex oxides have attracted intense research in the past decade. Yet, the fundamental mechanisms underpinning functionality are often elusive, especially in doped manganites, limiting their implementation in functional electronic devices such as memristors and spin valves. Here, we present a local probe-based study on mixed-terminated $L a_{5 / 8} C a_{3 / 8} Mn O_{3}$ (LCMO) films, and reveal surface metallicity in a thin film grown by pulsed-laser deposition. Using first-principles density-functional theory calculations with Hubbard correction that are more accurate to capture effects of correlation in these systems, we show that for Ca-segregated (001) LCMO surfaces the (La,Ca)O-site terminated surfaces are half metallic due to delocalized Mn- $d$ states populating the Fermi level, whereas the ${MnO}_{2}$ -site terminated surfaces exhibit a half-metallic or insulating character depending on the type of surface reconstruction. Computations not only explain the current measurements, but also explain other recent surface measurements on LCMO thin films, leading to a coherent picture of how the crucial link between surface segregation and Jahn-Teller couplings in the manganese oxides tune the surface electronic/magnetic structure, thereby pointing to the fine control of transport and magnetism at the conductive oxide surface independent of the bulk.

Received 25 January 2018
Revised 7 August 2018

DOI:https://doi.org/10.1103/PhysRevMaterials.2.104418

Physics Subject Headings (PhySH)

Charge density waves Density of states Electron-phonon coupling

Scanning tunneling spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Rama K. Vasudevan^1,2,*, Hemant Dixit^3,†, Alexander Tselev⁴, Liang Qiao^1,‡, Tricia L. Meyer³, Valentino R. Cooper³, Arthur P. Baddorf^1,2, Ho Nyung Lee³, P. Ganesh^1,2,§, and Sergei V. Kalinin^1,2,¶

¹Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
²ORNL Institute for Functional Imaging of Materials, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
³Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
⁴Department of Physics and CICECO–Aveiro Institute of Materials, University of Aveiro, 3810-193 Aveiro, Portugal

^*These authors contributed equally to this work.
^†Present address: GLOBALFOUNDRIES, 400 Stone Break Rd Extension, Malta, NY 12020, USA.
^‡Present address: School of Materials, The University of Manchester, Manchester M13 9PL, United Kingdom.
^§ganeshp@ornl.gov
^¶sergei2@ornl.gov