Effect of oxygen content on the transport properties of LaTiO_3+β/2thin films

Abstract

The structural and transport properties of LaTiO(3+β/2) epitaxial thin films, grown at different oxygen pressures ranging from 6.6 × 10(-4) to 5 Pa, have been investigated. X-ray diffraction peaks of the films shift to lower angles with increasing oxygen pressure, indicative of a variation of the corresponding lattice spacing. All the films show T(2) dependence of resistivity over a large temperature range of ∼200 K, suggesting a band-filling-induced metallic Fermi-liquid behaviour. Upturns in resistivity have been revealed at low temperatures, which could be ascribed to the Anderson-localization effect caused by the cation vacancies. Furthermore, for the thin films grown at high oxygen pressures of 0.5 and 5 Pa, the dependence of resistivity on temperature shows a maximum at high temperatures. The maximum seems to support the argument that transition between t-orbital ordering and disordering plays an important role in dominating transport properties at high temperatures. Carrier density deduced from Hall coefficient increases with the decrease of oxygen content, and shows strong temperature dependence. From the experimental data, it can be asserted that in the LaTiO(3+β/2) thin films, besides the band filling effect, localization or disorder caused by La and Ti vacancy effects controls the unique transport properties.

Two-dimensional superconductivity at a Mott insulator/band insulator interface LaTiO3/SrTiO3

“…It is known that LaTiO 3 itself can be oxygen [20][21] or Sr doped 23 , and thus becomes metallic. The key question is therefore: does superconductivity take place within a doped Mott insulator layer, namely oxygen-or Sr-doped LaTiO 3 , or within a 2-DEG formed at the LaTiO 3 /SrTiO 3 interface, which extends mostly within the band insulator SrTiO 3 (ref.…”

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

“…Earlier studies on p ‐doping of LTO thin films report only small variations in resistivity or even never reach the truly undoped, i.e., insulating phase . These studies most probably lack the full control of the oxygen stoichiometry and suffer from unintended excess oxygen doping as discussed above.…”

“…Here, we report on the filling controlled MT in LaTiO 3+ x (LTO) thin films driven by excess oxygen doping. Despite the abundant literature on this prototypical Mott material, its tendency to overoxidize still remains an unresolved problem in the fabrication of LTO thin films that impedes a precise tuning of the material's electronic properties as desired for Mottronic applications . We address this issue and tame the overoxidation which allows us to fabricate fully stoichiometric LTO thin films and demonstrate that a controlled oxygen excess doping allows to tune the electronic properties as is required for a channel material for Mottronics.…”

“…The existence of these oxygen‐rich phases poses challenges for the fabrication of stoichiometric LaTiO 3 thin films, since the energetically favored valence is Ti 4+ and unintentional and uncontrolled overoxidation may easily occur. Earlier reports on the transport properties of LTO thin films may be corrupted by such effects, which are easily overlooked when the titanium valence is not directly characterized …”

“…Avoiding overoxidation, i.e., gaining control of the oxygen stoichiometry in LTO thin films is an essential prerequisite for controlled p ‐doping that has not yet been established . Due to the elevated temperatures required during thin‐film fabrication, substantial oxygen diffusion between substrate and film is expected .…”