201 research outputs found
Confinement and Superconductivity at the LaAlO3/SrTiO3 Interface
The interface between LaAlO3 and SrTiO3, two good band insulators, was found to be conducting
[1], and, in some doping range, superconducting with a maximum critical temperature of about 300
mK [2,3].
I will discuss in this presentation the electronic structure, superconductivity, and the Tc versus
doping phase diagram of LaAlO3/SrTiO3 and ((LaAlO3)0.5-(SrTiO3)0.5)-SrTiO3 interfaces. I will
also compare superconductivity at these interfaces with superconductivity in bulk doped SrTiO3 [4].
[1] A. Ohtomo, H. Y. Hwang, Nature 427, 423 (2004).
[2] N. Reyren, S. Thiel, A. D. Caviglia, L. Fitting Kourkoutis, G. Hammerl, C. Richter, C. W.
Schneider, T. Kopp, A.-S. Ruetschi, D. Jaccard, M. Gabay, D. A. Muller, J.-M. Triscone and J.
Mannhart, Science 317, 1196 (2007).
[3] A. Caviglia, S. Gariglio, N. Reyren, D. Jaccard, T. Schneider, M. Gabay, S. Thiel, G. Hammerl, J.
Mannhart, and J.-M. Triscone, Nature 456, 624 (2008).
[4] S. Gariglio, M. Gabay, and J.-M. Triscone, Review APL Materials, 4, 060701 (2016)
Tuning of the depolarization field and nanodomain structure in ferroelectric thin films
The screening efficiency of a metal-ferroelectric interface plays a critical
role in determining the polarization stability and hence the functional
properties of ferroelectric thin films. Imperfect screening leads to strong
depolarization fields that reduce the spontaneous polarization or drive the
formation of ferroelectric domains. We demonstrate that by modifying the
screening at the metal-ferroelectric interface through insertion of ultrathin
dielectric spacers, the strength of the depolarization field can be tuned and
thus used to control the formation of nanoscale domains. Using piezoresponse
force microscopy, we follow the evolution of the domain configurations as well
as polarization stability as a function of depolarization field strength.Comment: 19 pages, 7 figure
Proposed cavity Josephson plasmonics with complex-oxide heterostructures
We discuss how complex-oxide heterostructures that include high-Tc
superconducting cuprates can be used to realize an array of sub-millimeter
cavities that support Josephson plasmon polaritons. These cavities have several
attractive features for new types of light matter interaction studies and we
show that they promote "ultrastrong" coupling between THz frequency radiation
and Josephson plasmons. Cavity electrodynamics of Josephson plasmons allows to
manipulate the superconducting order-parameter phase coherence. As an example,
we discuss how it could be used to cool superconducting phase fluctuations with
light
Nanoscale studies of domain wall motion in epitaxial ferroelectric thin films
Atomic force microscopy was used to investigate ferroelectric switching and
nanoscale domain dynamics in epitaxial PbZr0.2Ti0.8O3 thin films. Measurements
of the writing time dependence of domain size reveal a two-step process in
which nucleation is followed by radial domain growth. During this growth, the
domain wall velocity exhibits a v ~ exp[-(1/E)^mu] dependence on the electric
field, characteristic of a creep process. The domain wall motion was analyzed
both in the context of stochastic nucleation in a periodic potential as well as
the canonical creep motion of an elastic manifold in a disorder potential. The
dimensionality of the films suggests that disorder is at the origin of the
observed domain wall creep. To investigate the effects of changing the disorder
in the films, defects were introduced during crystal growth (a-axis inclusions)
or by heavy ion irradiation, producing films with planar and columnar defects,
respectively. The presence of these defects was found to significantly decrease
the creep exponent mu, from 0.62 - 0.69 to 0.38 - 0.5 in the irradiated films
and 0.19 - 0.31 in the films containing a-axis inclusions.Comment: 13 pages, 15 figures, to be published in J. App. Phys. special issue
on ferroelectric
Probing Quantum Confinement and Electronic Structure at Polar Oxide Interfaces
Polar discontinuities occurring at interfaces between two different materials
constitute both a challenge and an opportunity in the study and application of
a variety of devices. In order to cure the large electric field occurring in
such structures, a reconfiguration of the charge landscape sets in at the
interface via chemical modifications, adsorbates or charge transfer. In the
latter case, one may expect a local electronic doping of one material: one
sparkling example is the two-dimensional electron liquid (2DEL) appearing in
SrTiO once covered by a polar LaAlO layer. Here we show that tuning the
formal polarisation of a (La,Al)(Sr,Ti)O (LASTO:) overlayer
through chemical composition modifies the quantum confinement of the 2DEL in
SrTiO and its electronic band structure. The analysis of the behaviour in
magnetic field of superconducting field-effect devices reveals, in agreement
with calculations and self-consistent Poisson-Schr\"odinger
modelling, that quantum confinement and energy splitting between electronic
bands of different symmetries strongly depend on interface charge densities.
These results not only strongly support the polar discontinuity mechanisms with
a full charge transfer to explain the origin of the 2DEL at the celebrated
LaAlO/SrTiO interface, but also demonstrate an effective tool for
tailoring the electronic structure at oxide interfaces.Comment: 18 pages, 4 figures, 1 ancillary file (Supporting Information
High sensitivity variable-temperature infrared nanoscopy of conducting oxide interfaces
Probing the local transport properties of two-dimensional electron systems
(2DES) confined at buried interfaces requires a non-invasive technique with a
high spatial resolution operating in a broad temperature range. In this paper,
we investigate the scattering-type scanning near field optical microscopy as a
tool for studying the conducting LaAlO3/SrTiO3 interface from room temperature
down to 6 K. We show that the near-field optical signal, in particular its
phase component, is highly sensitive to the transport properties of the
electron system present at the interface. Our modelling reveals that such
sensitivity originates from the interaction of the AFM tip with coupled
plasmon-phonon modes with a small penetration depth. The model allows us to
quantitatively correlate changes in the optical signal with the variation of
the 2DES transport properties induced by cooling and by electrostatic gating.
To probe the spatial resolution of the technique, we image conducting
nano-channels written in insulating heterostructures with a voltage-biased tip
of an atomic force microscope.Comment: 19 pages, 5 figure
Fabricating Superconducting Interfaces between Artificially-Grown LaAlO and SrTiO Thin Films
Realization of a fully metallic two-dimensional electron gas at the interface
between artificially-grown LaAlO and SrTiO thin films has been an
exciting challenge. Here we present for the first time the successful
realization of a superconducting 2DEG at interfaces between artificially-grown
LaAlO and SrTiO thin films. Our results highlight the importance of two
factors-the growth temperature and the SrTiO termination. We use local
friction force microscopy and transport measurements to determine that in
normal growth conditions the absence of a robust metallic state at low
temperature in the artificially-grown LaAlO/SrTiO interface is due to
the nanoscale SrO segregation occurring on the SrTiO film surface during
the growth and the associated defects in the SrTiO film. By adopting an
extremely high SrTiO growth temperature, we demonstrate a way to realize
metallic, down to the lowest temperature, and superconducting 2DEG at
interfaces between LaAlO layers and artificially-grown SrTiO thin
films. This study paves the way to the realization of functional
LaAlO/SrTiO superlattices and/or artificial LaAlO/SrTiO
interfaces on other substrates
Monodomain to polydomain transition in ferroelectric PbTiO3 thin films with La0.67Sr0.3MnO3 electrodes
Finite size effects in ferroelectric thin films have been probed in a series
of epitaxial perovskite c-axis oriented PbTiO3 films grown on thin
La0.67Sr0.33MnO3 epitaxial electrodes. The film thickness ranges from 480 down
to 28 A (7 unit cells). The evolution of the film tetragonality c/a, studied
using high resolution x-ray diffraction measurements, shows first a decrease of
c/a with decreasing film thickness followed by a recovery of c/a at small
thicknesses. This recovery is accompanied by a change from a monodomain to a
polydomain configuration of the polarization, as directly demonstrated by
piezoresponse atomic force microscopy measurements
Artificial quantum confinement in LAO3/STO heterostructure
Heterostructures of transition metal oxides (TMO) perovskites represent an
ideal platform to explore exotic phenomena involving the complex interplay
between the spin, charge, orbital and lattice degrees of freedom available in
these compounds. At the interface between such materials, this interplay can
lead to phenomena that are present in none of the original constituents such as
the formation of the interfacial 2D electron system (2DES) discovered at the
LAO3/STO3 (LAO/STO) interface. In samples prepared by growing a LAO layer onto
a STO substrate, the 2DES is confined in a band bending potential well, whose
width is set by the interface charge density and the STO dielectric properties,
and determines the electronic band structure. Growing LAO (2 nm) /STO (x
nm)/LAO (2 nm) heterostructures on STO substrates allows us to control the
extension of the confining potential of the top 2DES via the thickness of the
STO layer. In such samples, we explore the dependence of the electronic
structure on the width of the confining potential using soft X-ray ARPES
combined with ab-initio calculations. The results indicate that varying the
thickness of the STO film modifies the quantization of the 3d t2g bands and,
interestingly, redistributes the charge between the dxy and dxz/dyz bands
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