31 research outputs found
Interface-engineered hole doping in Sr2IrO4/LaNiO3 heterostructure
The relativistic Mott insulator Sr2IrO4 driven by large spin-orbit
interaction is known for the Jeff = 1/2 antiferromagnetic state which closely
resembles the electronic structure of parent compounds of superconducting
cuprates. Here, we report the realization of hole-doped Sr2IrO4 by means of
interfacial charge transfer in Sr2IrO4/LaNiO3 heterostructures. X-ray
photoelectron spectroscopy on Ir 4f edge along with the X-ray absorption
spectroscopy at Ni L2 edge confirmed that 5d electrons from Ir sites are
transferred onto Ni sites, leading to markedly electronic reconstruction at the
interface. Although the Sr2IrO4/LaNiO3 heterostructure remains non-metallic, we
reveal that the transport behavior is no longer described by the Mott variable
range hopping mode, but by the Efros-Shklovskii model. These findings highlight
a powerful utility of interfaces to realize emerging electronic states of the
Ruddlesden-Popper phases of Ir-based oxides.Comment: 9 pages including 3 figures and reference
Orientation-dependent stabilization of MgCrO spinel thin films
ABO normal spinels with a magnetic B site can host a variety of
magnetic and orbital frustrations leading to spin-liquid phases and
field-induced phase transitions. Here we report the first epitaxial growth of
(111)-oriented MgCrO thin films. By characterizing the structural and
electronic properties of films grown along (001) and (111) directions, the
influence of growth orientation has been studied. Despite distinctly different
growth modes observed during deposition, the comprehensive characterization
reveals no measurable disorder in the cation distribution nor multivalency
issue for Cr ions in either orientation. Contrary to a naive expectation, the
(111) stabilized films exhibit a smoother surface and a higher degree of
crystallinity than (001)-oriented films. The preference in growth orientation
is explained within the framework of heteroepitaxial stabilization in
connection to a significantly lower (111) surface energy. These findings open
broad opportunities in the fabrication of 2D kagome-triangular heterostructures
with emergent magnetic behavior inaccessible in bulk crystals
Epitaxial stabilization of the frustrated Ge-based spinel thin films
Frustrated magnets can host numerous exotic many-body quantum and topological
phenomena. GeNiO is a three dimensional frustrated magnet with an
unusual two-stage transition to the two-dimensional antiferromagnetic ground
state, while GeCuO is a high-pressure phase with a strongly
tetragonally elongated spinel structure and magnetic lattice formed by
CuO linear chains with frustrated exchange interactions and exotic magnetic
behavior. Here we report on the first thin-film epitaxial stabilization of
these two compounds. Developed growth mode, surface morphology, crystal
structure and copper valence state were characterized by in-situ reflection
high-energy electron diffraction, atomic force microscopy, X-ray reflectivity,
X-ray diffraction, X-ray photoelectron spectroscopy and resonant X-ray
absorption spectroscopy. Our results pave an alternative route to the
comprehensive investigation of the puzzling magnetic properties of these
compounds and exploration of novel emergent features driven by strain
Anomalous orbital structure in two-dimensional titanium dichalcogenides
Generally, lattice distortions play a key role in determining the ground
states of materials. Although it is well known that trigonal distortions are
generic to most two-dimensional transition metal dichalcogenides, the impact of
this structural distortion on the electronic structure has not been understood
conclusively. Here, by using a combination of polarization dependent X-ray
absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS) and
atomic multiplet cluster calculations, we have investigated the electronic
structure of titanium dichalcogenides TiX2 (X=S, Se, Te), where the magnitude
of the trigonal distortion increase monotonically from S to Se and Te. Our
results reveal the presence of an anomalous and large crystal filed splitting.
This unusual kind of crystal field splitting is likely responsible for the
unconventional electronic structure of TiX2 compounds. Our results also
indicate the drawback of the distorted crystal field picture in explaining the
observed electronic ground state of these materials and emphasize the key
importance of metal-ligand hybridization and electronic correlation in defining
the electronic structures near Fermi energy
Synthesis of epitaxial magnetic pyrochlore heterojunctions
The synthesis of stoichiometric and epitaxial pyrochlore iridate thin films
presents significant challenges yet is critical for unlocking experimental
access to novel topological and magnetic states. Towards this goal, we unveil
an in-situ two-stage growth mechanism that facilitates the synthesis of
high-quality oriented pyrochlore iridate thin films. The growth starts with the
deposition of a pyrochlore titanate as an active iso-structural template,
followed by the application of an in-situ solid phase epitaxy technique in the
second stage to accomplish the formation of single crystalline, large-area
films. This novel protocol ensures the preservation of stoichiometry and
structural homogeneity, leading to a marked improvement in surface and
interface qualities over previously reported methods. The success of this
synthesis approach is attributed to the application of directional laser-heat
annealing, which effectively reorganizes the continuous random network of ions
into a crystalline structure, as evidenced by our comprehensive analysis of the
growth kinetics. This new synthesis approach advances our understanding of
pyrochlore iridate film fabrication and opens a new perspective for
investigating their unique physical properties.Comment: 11 pages, 4 figures; supplementary materials (1 table, 6 figures