Tailoring Materials for Mottronics: Excess Oxygen Doping of a Prototypical Mott Insulator

Abstract

The Mott transistor is a paradigm for a new class of electronic devices-often referred to by the term Mottronics-which are based on charge correlations between the electrons. Since correlation-induced insulating phases of most oxide compounds are usually very robust, new methods have to be developed to push such materials right to the boundary to the metallic phase in order to enable the metal-insulator transition to be switched by electric gating. Here, it is demonstrated that thin films of the prototypical Mott insulator LaTiO grown by pulsed laser deposition under oxygen atmosphere are readily tuned by excess oxygen doping across the line of the band-filling controlled Mott transition in the electronic phase diagram. The detected insulator to metal transition is characterized by a strong change in resistivity of several orders of magnitude. The use of suitable substrates and capping layers to inhibit oxygen diffusion facilitates full control of the oxygen content and renders the films stable against exposure to ambient conditions. These achievements represent a significant advancement in control and tuning of the electronic properties of LaTiO thin films making it a promising channel material in future Mottronic devices.

Co valence transformation in isopolarLaCoO3/LaTiO3perovskite heterostructures via interfacial engineering

“…These in-situ XPS experiments -in line with those of Ref. [23] -show that Ti 3+ in LTO films can certainly be generated, but in the context of this paper one should add under conditions that are too aggressively reducing for LCO to remain stable. In addition, to the true electron count in the LTO structures, it is also conceivable that Ni3d level in the LNO cap is positioned in energy such that it can act as an acceptor for electrons from the LTO, or indeed from the LCO.…”

“…This makes it unlikely the extra oxygen interstitials proposed in Ref. [23] could be present in our heterostructures at a density anywhere near that required to reach LaTiO 3.5 , as the STEM data show such a clean, non-reconstructed ABO 3 structure right across the heterointerface. Next, on the LCO side, also no deviations from the 113-perovskite structure are seen in the TEM imaging.…”

“…that we chose to grow the samples in, one could expect the formation of LaTiO 3+d and LaCoO 3d , as this has been seen in the growth of each material as a 'stand-alone' system [23,25]. Thus, in our heterostructures the possibilities are manifold: (a) a 3d 7 |3d 0 LaCoO 2.5 -LaTiO 3.5 interface, even (b) a 3d 7 |3d 1 LaCoO 2.5 -LaTiO 3 interface or the reverse: (c) a 3d 6 |3d 1 LaCoO 3 -LaTiO 3.5 interface.…”

“…The question of Ti 4+ in LTO has been addressed in part in Ref. [23], although the extra oxygen interstitials they propose would seem difficult to fit into 113-ABO 3 structure at the required density. In Fig.…”

“…Subsequently, a 30 unit cell (uc) thick layer of LaAlO 3 (LAO) was grown. This served to (a) enable an accurate calibration of the PLD set-up as LAO grows very well in a layer-by-layer manner; (b) prevent formation of a polar-interfacedriven charge transfer involving the LCO or LTO (both of which are polar) by separating them far from the non-polar STO, (c) mask the Ti states of the STO substrate in the soft X-ray absorption experiments and (d) block transport of oxygen from the STO substrate into the LTO film [ 23 ]. After growth of the LTO, LCO or combinations thereof, a 5 uc LaNiO 3 (LNO) layer was added as a cap, so as to enable ambient transfer of the samples to the synchrotron and reduce the chance of charging effects.…”