Reversible and Persistent Photoconductivity at the NdGaO3/SrTiO3 Conducting Interface

Source: arXiv


The interface between the band gap insulators LaAlO3 and SrTiO3 is known to
host a highly mobile two-dimensional electron gas. Here we report on the
fabrication and characterization of the NdGaO3/SrTiO3 interface, that shares
with LaAlO3/SrTiO3 an all-perovskite structure, the insulating nature of the
single building block and the polar-non polar character. Our work demonstrates
that in NdGaO3/SrTiO3 a metallic layer of mobile electrons is formed, with
properties comparable to LaAlO3/SrTiO3. The localization of the injected
electrons at the Ti sites, within a few unit cells from the interface, was
proved by Atomic-scale-resolved EELS analyses. The electric transport and
photoconduction of samples were also investigated. We found that irradiation by
photons below the SrTiO3 gap does not increase the carrier density, but
slightly enhances low temperature mobility. A giant persistent
photoconductivity effect was instead observed, even under irradiation by low
energy photons, in highly resistive samples fabricated at non-optimal
conditions. We discuss the results in the light of different mechanisms
proposed for the two-dimensional electron gas formation. Both the ordinary and
the persistent photoconductivity in these systems are addressed and analyzed.

Download full-text


Available from: Claudia Cantoni
  • [Show abstract] [Hide abstract]
    ABSTRACT: The spin polarized two dimensional electron gas in the correlated ABO3/SrTiO3 (A = Pr, Nd and B = Al, Ga) heterostructures is investigated by ab-initio calculations using density functional theory. Structural relaxation shows a strong buckling at and near the TiO2 terminated n-type interface (IFs) due to significant TiO6 octahedral distortions. We find in all cases, metallic states in a very narrow region of the SrTiO3, in agreement with experimental results. We demonstrate that the interface magnetism strongly reacts to the magnitude of the lattice strain. The orbital occupations and, hence, the charge carrier density change systematically as a function of the lattice mismatch between the component materials.
    No preview · Article · Apr 2013 · Applied Physics Letters
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Novel properties arising at interfaces between transition metal oxides, particularly the conductivity at the interface of LaAlO3 (LAO) and SrTiO3 (STO) band insulators, have generated new paradigms, challenges, and opportunities in condensed matter physics. Conventional transport measurements have established that intrinsic conductivity appears in LAO/STO interfaces when the LAO film matches or exceeds a critical thickness of 4 unit cells (uc). Recently, a number of experiments raise important questions about the role of the LAO film, the influence of photons, and the effective differences between vacuum/STO and LAO/STO, both above and below the standard critical thickness. Here, using angle-resolved photoemission spectroscopy (ARPES) on in situ prepared samples, as well as resonant inelastic x-ray scattering (RIXS), we study how the metallic STO surface state evolves during the growth of a crystalline LAO film. In all the samples, the character of the conduction bands, their carrier densities, the Ti3+ crystal fields, and the responses to photon irradiation bear strong similarities. However, LAO/STO interfaces exhibit intrinsic instability toward in-plane folding of the Fermi surface at and above the 4-uc thickness threshold. This ordering distinguishes these heterostructures from bare STO and sub-critical-thickness LAO/STO and coincides with the onset of unique properties such as magnetism and built-in conductivity.
    Full-text · Article · Apr 2013