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The physics of conducting interfaces in insulating heterostructures

Applicant Willmott Philip
Number 126901
Funding scheme Project funding (Div. I-III)
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Condensed Matter Physics
Start/End 01.05.2010 - 30.04.2013
Approved amount 171'914.00
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Keywords (8)

complex metal oxides; strongly correlated electron-systems; synchrotron radiation; surface x-ray diffraction; interfacial physics; Interfaces; Thin films; Surface diffraction

Lay Summary (English)

Lead
Lay summary
The physical properties of materials at surfaces and interfaces can often be significantly different than those of the bulk material. The reason for this is that in these regions, the binding strengths, number of bonds, and local chemistry can all be quite distinct than those of the bulk phase. The valence electrons involved in the chemical bonds rearrange in order to minimize their energy, which inevitably influences the electronic properties in this region. A dramatic example of this was the discovery in 2004 of a highly conducting two-dimensional layer at the interface between SrTiO3 and LaAlO3. As near-future devices are expected to have characteristic lengths of only a few nanometers, this system is of particular interest as a prototype for controlling conducting layers based on materials other than silicon. The physics responsible for this phenomenon remains highly contentious. It is generally agreed, however, that a prerequisite for unravelling the causes for this conducting layer is a detailed knowledge of the atomic structure. This type of material (so-called "perovskites") are characterized by being particularly sensitive to changes in bond lengths and angles as small as a few pm and one or two degrees, respectively. The only experimental method capable of resolving the structure to this level of accuracy is surface x-ray diffraction (SXRD). This project is concerned with the synthesis and analysis using SXRD of different combinations of SrTiO3 and LaAlO3, especially targeted to better understand the underlying physics of this and similar systems.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Interface fermi states of LaAlO3/SrTiO3 and related heterostructures
Cancellieri C, Reinle-Schmitt M L, Kobayashi M, Strocov V N, Schmitt T, Willmott P R, Gariglio S, Triscone J-M (2013), Interface fermi states of LaAlO3/SrTiO3 and related heterostructures, in Physical Review Letters, 110(13), 137601.
Tunable conductivity threshold at polar interfaces
Reinle-Schmitt M L, Cancellieri C, Li D, Fontaine D, Medarde M, Pomjakushina E, Schneider C W, Gariglio S, Ghosez P, Triscone J-M, Willmott P R (2013), Tunable conductivity threshold at polar interfaces, in Nature Communications , 3, 932.

Collaboration

Group / person Country
Types of collaboration
University of Geneva, DPMC Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
ADRESS beamline, Paul Scherrer Institut Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Physique Théorique des Matériaux, Université de Liège Belgium (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Workshop on Oxide Electronics 19 Talk given at a conference Oxide interfaces 30.09.2012 Apeldoorn, Netherlands, Netherlands Reinle-Schmitt Mathilde;
Swiss Physical Society Meeting Talk given at a conference 2D gas at oxide interfaces 21.06.2012 ETHZ, Zuerich, CH, Switzerland Reinle-Schmitt Mathilde;


Communication with the public

Communication Title Media Place Year
New media (web, blogs, podcasts, news feeds etc.) Controversy clarified: Why two insulators together can transport electricity PSI Press and Media German-speaking Switzerland 2012

Associated projects

Number Title Start Funding scheme
117615 Interfacial properties of perovskite thin films 01.10.2007 Project funding (Div. I-III)
137507 Direct Methods Applied to Oxide Heterostructures 01.01.2012 Project funding (Div. I-III)
146015 The physics of conducting interfaces in insulating heterostructures 01.05.2013 Project funding (Div. I-III)

Abstract

Since its discovery in 2004, the phenomenon of the formation of 2-dimensional conducting layers at the interface between two insulating metal oxides has been the subject of intense research. The reason for the enormous interest these systems have provoked is due to their possible application in novel and highly versatile electronic applications and circuitry based on metal oxides, for which a very broad range of physical properties exist, despite their often very similar crystallographic structures. However, in 2009, there remain many fundamental questions, as new and unexpected results are reported. One of the problems in investigating such systems is that the regions of interest, that is, the interface, is by its very nature embedded in a solid. This makes electronic studies such as photoelectron spectroscopy very problematic (and is further exacerbated by the fact that the conducting interface lies between insulating layers), while scanning probe techniques such as scanning tunneling microscopy or atomic force microscopy are completely excluded. On the other hand, structural studies using x-rays provide a very powerful probe, as x-rays can penetrate deeply into material, and their wavelengths are such that sub-atomic resolution is provided. The Swiss Light Source at the Paul Scherrer Institut provides highly brilliant x-radiation, ideal for such investigations. At the Surface Diffraction station of the Materials Science beamline at the SLS (of which the applicant is the Beamline Manager), a unique combination of experimental equipment exists, whereby surface x-ray diffraction (SXRD) can be performed on these interfaces and, importantly, this can be done as the interface is being fabricated, such that the change in the structure can be monitored in steps well under a single monolayer of growth. This has been made possible on the one hand by a custom-made and dedicated growth chamber, with exactly this application in mind, and on the other, on the availability of a novel photon-counting 2-D x-ray pixel detector, a development which has revolutionized SXRD in the last three to four years. Very recent results by the group of the applicant for this grant have demonstrated that a novel and as yet unconsidered process is responsible for the formation of 2-dimensional conductivity. It is the goal of this project to investigate this using SXRD and the available facilities at the Surface Diffraction station of the SLS, both to probe the growth dynamics and surface/interfacial chemical kinetics, and to provide a detailed structural model at all stages of the formation of the conducting interface.
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