137 research outputs found
Nanoscale Quantification of Octahedral Tilts in Perovskite Films
NiO6-octahedral tilts in ultrathin LaNiO3 films were studied using position
averaged convergent beam electron diffraction (PACBED) in scanning transmission
electron microscopy. Both the type and magnitude of the octahedral tilts were
determined by comparing PACBED experiments to frozen phonon multislice
simulations. It is shown that the out-of-plane octahedral tilt of an epitaxial
film under biaxial tensile stress (0.78 % in-plane tensile strain) increases by
~ 20%, while the in-plane rotation decreases by ~ 80%, compared to the
unstrained bulk material.Comment: The manuscript has been accepted by Applied Physics Letters. After it
is published, it will be found at: http://apl.aip.org
A heterojunction modulation-doped Mott transistor
A heterojunction Mott field effect transistor (FET) is proposed that consists
of an epitaxial channel material that exhibits an electron-correlation-induced
Mott metal-to-insulator transition. The Mott material is remotely (modulation)
doped with a degenerately doped conventional band insulator. An applied voltage
modulates the electron transfer from the doped band insulator to the Mott
material and produces transistor action by inducing an insulator-to-metal
transition. Materials parameters from rare-earth nickelates and SrTiO3 are used
to assess the potential of the "modulation-doped Mott FET" (ModMottFET or
MMFET) as a next-generation switch. It is shown that the MMFET is characterized
by unique "charge gain" characteristics as well as competitive
transconductance, small signal gain and current drive.Comment: The article has been accepted by Journal of Applied Physics. After it
is published, it will be found at: http://jap.aip.org
Structural origins of the properties of rare earth nickelate superlattices
NiO6 octahedral tilts in the LaNiO3/SrTiO3 superlattices are quantified using
position averaged convergent beam electron diffraction in scanning transmission
electron microscopy. It is shown that maintaining oxygen octahedra connectivity
across the interface controls the octahedral tilts in the LaNiO3 layers, their
lattice parameters and their transport properties. Unlike films and layers that
are connected on one side to the substrate, subsequent LaNiO3 layers in the
superlattice exhibit a relaxation of octahedral tilts towards bulk values. This
relaxation is facilitated by correlated tilts in SrTiO3 layers and is
correlated with the conductivity enhancement of the LaNiO3 layers in the
superlattices relative to individual films.Comment: Accepted for publication in Physical Review B (Rapid Communication
Probing the metal-insulator transition of NdNiO3 by electrostatic doping
Modulation of the charge carrier density in a Mott material by remote doping
from a highly doped conventional band insulator is proposed to test theoretical
predictions of band filling control of the Mott metal-insulator transition
without introducing lattice distortions or disorder, as is the case for
chemical doping. The approach is experimentally tested using ultrathin (2.5 nm)
NdNiO3 films that are epitaxially grown on La-doped SrTiO3 films. We show that
remote doping systematically changes the charge carrier density in the NdNiO3
film and causes a moderate shift in the metal-insulator transition temperature.
These results are discussed in the context of theoretical models of this class
of materials exhibiting a metal-insulator transition.Comment: The article has been accepted by Applied Physics Letters. After it is
published, it will be found at http://apl.aip.org
Orbital-selective Mott and Peierls transition in HxVO2
Materials displaying metal-insulator transitions (MITs) as a function of external parameters such as temperature, pressure, or composition are most intriguing from the fundamental point of view and also hold high promise for applications. Vanadium dioxide (VO2) is one of the most prominent examples of MIT having prospective applications ranging from intelligent coatings, infrared sensing, or imaging, to Mott memory and neuromorphic devices. The key aspects conditioning possible applications are the controllability and reversibility of the transition. Here we present an intriguing MIT in hydrogenated vanadium dioxide, HxVO2. The transition relies on an increase of the electron occupancy through hydrogenation on the transition metal vanadium, driving the system insulating by a hybrid of two distinct MIT mechanisms. The insulating phase observed in HVO2 with a nominal d2 electronic configuration contrasts with other rutile d2 systems, most of which are metallic. Using spectroscopic tools and state-of-the-art many-body electronic structure calculations, our investigation reveals a correlation-enhanced Peierls and a Mott transition taking place in an orbital-selective manner cooperate to stabilize an insulating phase. The identification of the hybrid mechanism for MIT controlled by hydrogenation opens the way to radically design strategies for future correlated oxide devices by controlling phase reversibly while maintaining high crystallinity
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