Colloquium: Emergent properties in plane view: Strong correlations at oxide interfaces

Jak Chakhalian, John W. Freeland, Andrew J. Millis, Christos Panagopoulos, and James M. Rondinelli

Rev. Mod. Phys. 86, 1189 – Published 13 October 2014

Abstract

Finding new collective electronic states in materials is one of the fundamental goals of condensed matter physics. Atomic-scale superlattices formed from transition metal oxides are a particularly appealing hunting ground for new physics. In bulk form, transition metal oxides exhibit a remarkable range of magnetic, superconducting, and multiferroic phases that are of great scientific interest and are potentially capable of providing innovative energy, security, electronics, and medical technology platforms. In superlattices new states may emerge at the interfaces where dissimilar materials meet. This Colloquium illustrates the essential features that make transition metal oxide-based heterostructures an appealing discovery platform for emergent properties with a few selected examples, showing how charge redistributes, magnetism and orbital polarization arises, and ferroelectric order emerges from heterostructures comprised of oxide components with nominally contradictory behavior with the aim providing insight into the creation and control of novel behavior at oxide interfaces by suitable mechanical, electrical, or optical boundary conditions and excitations.

Received 24 December 2013

DOI:https://doi.org/10.1103/RevModPhys.86.1189

Authors & Affiliations

Jak Chakhalian

Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA

John W. Freeland

Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA

Andrew J. Millis

Department of Physics, Columbia University, 538 West 120th Street, New York, New York 10027, USA

Christos Panagopoulos

School of Physical and Mathematical Sciences, Division of Physics and Applied Physics, Nanyang Technological University, 637371 Singapore

James M. Rondinelli^*

Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104, USA

^*Present address: Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.

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Vol. 86, Iss. 4 — October - December 2014

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Images

Figure 1
Anatomy of an oxide heterointerface: an illustration showing the interplay between different degrees of freedom (charge, spin, and lattice) at a coherently grown interface between ferromagnetic ${La}_{2 / 3} {Ca}_{1 / 3} {MnO}_{3}$ and superconducting ${YBa}_{2} {Cu}_{3} O_{7 - x}$ . The electron micrograph is reproduced from [35], where each color represents a different chemical species.
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Figure 2
Electronic structure of Cu in a ${La}_{2 / 3} {Ca}_{1 / 3} {MnO}_{3} / {YBa}_{2} {Cu}_{3} O_{7 - x}$ heterostructure, determined from x-ray linear dichroism (XLD) and x-ray magnetic circular dichroism (XMCD) measurements. XLD spectra taken on the Cu $L_{3}$ edge at temperature $T = 15 K$ with the electric-field vector $E ∥ a b$ plane and $E ∥ c$ plane, taken in (a) bulk and (b) interface sensitive modes. The main peak (“white line”) in (b) is shifted toward higher energies, indicating a lower charge state of Cu at the interface. XMCD spectra measured at the Cu and Mn $L_{3}$ edges in (c) recorded at $T = 15 K$ in a 5 T applied magnetic field demonstrating that the interfacial copper cations exhibit a nonzero ferromagnetic local moment, whereas in bulk the antiferromagnetic coupling leads to a net magnetization of zero.
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Figure 3
(a) Schematic of cross-sectional scanning tunneling microscopy (XSTM) measurements performed on an LCMOand YBCO superlattice grown on a Nb-doped STO substrate. (b) The spatial evolution of the $d I / d V$ spectra averaged across the two identically terminated heterointerfaces reveals that the electronic transition is more abrupt for the bottom interface (right arrow) than the top, broader, interface (left arrow). The dots represent the voltage of the minimum in the density of states. From [35].
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Figure 4
(a) Schematic crystal structure showing canted spins (arrows) within the ${MnO}_{6}$ octahedra of ${CaMnO}_{3}$ at the interface of the quantum-well structure with metallic ${CaRuO}_{3}$ . The canting arises from electron transfer owing to the Ohmic contact. (b) X-ray resonant magnetic scattering data showing a large magnetic signature arising from the FM alignment of spins at the interface in the presence of a magnetic field [see associated data in 50].
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Figure 5
Ferroelectric and magnetoelectric properties of the $[({NdMnO}_{3})_{n} / ({SrMnO}_{3})_{n} / ({LaMnO}_{3})_{n}]_{m}$ superlattice, where ( $n, m$ ) denotes the specfic superlattice structure. (a) Schematic $[({NdMnO}_{3})_{5} / ({SrMnO}_{3})_{5} / ({LaMnO}_{3})_{5}]_{8}$ superlattice on single-crystalline ${SrTiO}_{3}$ substrate with the metal-oxygen octahedra and $A$ cations emphasized. The arrays of the arrows in (b) represent the corresponding antiferromagnetic spin arrangements for each component of the heterostructure. (c) Temperature ( $T$ ) dependence of the electric polarization ( $P$ ) measured in a superlattice of period (22,2) using the pyroelectric technique for a typical electric field ( $E_{a}$ ) of $+ 100 V {cm}^{- 1}$ (middle curve) and $- 100 V {cm}^{- 1}$ (bottom curve) applied perpendicular to the plane of the superlattice layering. The temperature-dependent electric polarization under a magnetic field $H = 6 T$ applied parallel to the plane of the superlattice layering (top curve) reveals strong magnetoelectric coupling. (d) Normalized relative change in the electric polarization at fixed electric and magnetic fields for various superlattices. Adapted [147].
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