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

Electric-Field-Induced Phase Transition in VO2 Thin Film Using All-Solid-State 3-Terminal Proton Transistor

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Low-temperature Fabrication of NbOx Selector Device with Steep Switching, Low Off-current and High Ion/Ioff by Pulsed Laser Annealing

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