178 research outputs found
Sub-monolayer nucleation and growth of complex oxide heterostructures at high supersaturation and rapid flux modulation
We report on the non-trivial nanoscale kinetics of the deposition of novel
complex oxide heterostructures composed of a unit-cell thick correlated metal
LaNiO3 and dielectric LaAlO3. The multilayers demonstrate exceptionally good
crystallinity and surface morphology maintained over the large number of
layers, as confirmed by AFM, RHEED, and synchrotron X-ray diffraction. To
elucidate the physics behind the growth, the temperature of the substrate and
the deposition rate were varied over a wide range and the results were treated
in the framework of a two-layer model. These results are of fundamental
importance for synthesis of new phases of complex oxide heterostructures.Comment: 13 pages, 6 figure
Effect of polar discontinuity on the growth of LaNiO3/LaAlO3 superlattices
We have conducted a detailed microscopic investigation of [LaNiO3(1
u.c.)/LaAlO3(1 u.c.)]N superlattices grown on (001) SrTiO3 and LaAlO3 to
explore the influence of polar mismatch on the resulting electronic and
structural properties. Our data demonstrate that the initial growth on the
non-polar SrTiO3 surface leads to a rough morphology and unusual 2+ valence of
Ni in the first LaNiO3 layer, which is not observed after growth on the polar
surface of LaAlO3. A newly devised model suggests that the polar mismatch can
be resolved if the perovskite layers grow with an excess of LaO, which also
accounts for the observed electronic, chemical, and structural effects.Comment: 3 pages, 3 figure
Orbital control in strained ultra-thin LaNiO/LaAlO superlattices
In pursuit of rational control of orbital polarization, we present a combined
experimental and theoretical study of single unit cell superlattices of the
correlated metal LaNiO and the band insulator LaAlO. Polarized x-ray
absorption spectra show a distinct asymmetry in the orbital response under
strain. A splitting of orbital energies consistent with octahedral distortions
is found for the case of compressive strain. In sharp contrast, for tensile
strain, no splitting is found although a strong orbital polarization is
present. Density functional theory calculations including a Hubbard U term
reveal that this asymmetry is a result of the interplay of strain and
confinement induces octahedral rotations and distortions and altered covalency
in the bonding across the interfacial Ni-O-Al apical oxygen, leading to a
charge disporportionation at the Ni sites for tensile strain.Comment: 4 pages. 5 figure
Epitaxial strain modulated electronic properties of interface controlled nickelate superlattice
Perovskite nickelate heterostructure consisting of single unit cell of
EuNiO and LaNiO have been grown on a set of single crystalline
substrates by pulsed laser interval deposition to investigate the effect of
epitaxial strain on electronic and magnetic properties at the extreme interface
limit. Despite the variation of substrate in-plane lattice constants and
lattice symmetry, the structural response to heterostructuring is primarily
controlled by the presence of EuNiO layer. In sharp contrast to bulk
LaNiO or EuNiO, the superlattices grown under tensile strains exhibit
metal to insulator transition (MIT) below room temperature. The onset of
magnetic and electronic transitions associated with the MIT can be further
separated by application of large tensile strain. Furthermore, these
transitions can be entirely suppressed by very small compressive strain. X-ray
resonant absorption spectroscopy measurements reveal that such
strain-controlled MIT is directly linked to strain induced self-doping effect
without any chemical doping.Comment: Accepted in Phys. Rev.
Strain-mediated metal-insulator transition in epitaxial ultra-thin films of NdNiO3
We have synthesized epitaxial NdNiO ultra-thin films in a
layer-by-layer growth mode under tensile and compressive strain on SrTiO
(001) and LaAlO (001), respectively. A combination of X-ray diffraction,
temperature dependent resistivity, and soft X-ray absorption spectroscopy has
been applied to elucidate electronic and structural properties of the samples.
In contrast to the bulk NdNiO, the metal-insulator transition under
compressive strain is found to be completely quenched, while the transition
remains under the tensile strain albeit modified from the bulk behavior.Comment: 4 pages, 4 figure
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