Metal-insulator transition induced in CaVO3 thin films

Abstract

Stoichiometric CaVO3 (CVO) thin films of various thicknesses were grown on single crystal SrTiO3 (STO) (001) substrates using a pulsed electron-beam deposition technique. The CVO films were capped with a 2.5 nm STO layer. We observed a temperature driven metal-insulator transition (MIT) in CVO films with thicknesses below 4 nm that was not observed in either thick CVO films or STO films. The emergence of this MIT can be attributed to the reduction in effective bandwidth due to a crossover from a three-dimensional metal to a two-dimensional insulator. The insulating phase was only induced with a drive current below 0.1 μA. X-ray absorption measurements indicated different electronic structures for thick and very thin films of CVO. Compared with the thick film (∼60 nm), thin films of CVO (2–4 nm) were more two-dimensional with the V charge state closer to V4+.

Electronic localization in CaVO3 films via bandwidth control

“…film was too insulating to be measured using our setup). The overall behaviour is similar to that previously reported for CaVO3 films [6]. Comparison of RHEED patterns recorded at room temperature after deposition of 15 u.c.…”

Metal-insulator transition in CaVO3 thin films: Interplay between epitaxial strain, dimensional confinement, and surface effects

“…Strain relaxation has also been confirmed for a 53 nm thick film investigated in Ref. 9. However, the strain states of the thinner films have not been characterized.…”

“…In Ref. 9, the thickness-dependent MIT has been attributed to a reduction of the effective bandwidth, resulting from a dimensional crossover from 3D to 2D. However, an alternative scenario for the observed MIT, related to a thickness-dependent relaxation of epitaxial strain, is outlined in the following.…”

“…The source for this MIT is often ascribed to confinement effects, which restrict electron movement to the in-plane directions of the film and lead to the formation of quantum well states [18,19]. However, the reported critical thicknesses for different materials are rather wide-spread, e.g., 3 respectively 5 unit cells for La 2/3 Ca 1/3 MnO 3 [12] and LaNiO 3 [14], compared to 4 nm (≈ 11 unit cells) in CaVO 3 [9]. Furthermore, even for different samples of the same material, the reported critical thicknesses can differ quite significantly, e.g., 2-3 unit cells for SrVO 3 in Ref.…”

Review on Electronic Correlations and the Metal-Insulator Transition in SrRuO3

“…SRO has a van Hove singularity at the proximity of E F (Dang et al, 2015;Han et al, 2016), and as the thickness approaches its ultrathin limit, where the dimensionality of the system changes from 3D to 2D (or even 1D, depending on the shapes of d-orbitals in t 2g symmetry), the DOS at the E F decreases (Chang et al, 2009;Verissimo et al, 2012). Similarly, SrVO 3 (SVO) undergoes a MIT at its ultrathin limit, and the MIT is ascribed to the shrunken dimensionality and corresponding van Hove peaks near the E F (Gu et al, 2013;Liebsch, 2003b;Yoshimatsu et al, 2010). Such a low-dimensional system also has low t 2g orbital degeneracy, making (U W ) c smaller than the bulk value (Gunnarsson et al, 1996).…”