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Register a new userStrain mediated suppression of the metal-insulator transition in EuNiO3 thin films
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Ultrathin epitaxial films of EuNiO3 were grown on a series of substrates traversing highly compressive (- 2.4%) to highly tensile (2.5%) lattice mismatch. X-ray diffraction measurements showed the expected c-lattice parameter shift for compressive strain, but no detectable shift for tensilely strained substrates, while reciprocal space mapping confirmed the tensile strained film maintained epitaxial coherence. Transport measurements showed a successively (from tensile to compressive) lower resistance and a complete suppression of the metalinsulator transition at highly compressive lattice mismatch. Corroborating these findings, X-ray absorption spectroscopy measurements revealed a strong multiplet splitting in the tensile samples that progressively weakens with increasing compressive strain that, combined with cluster calculations, showed enhanced covalence between Ni-d and O-p orbitals leads to the metallic state.
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We have synthesized epitaxial NdNiO$_{3}$ ultra-thin films in a layer-by-layer growth mode under tensile and compressive strain on SrTiO$_{3}$ (001) and LaAlO$_3$ (001), respectively. A combination of X-ray diffraction, temperature dependent resistivity, and soft X-ray absorption spectroscopy has been applied to elucidate electronic and structural properties of the samples. In contrast to the bulk NdNiO$_{3}$, the metal-insulator transition under compressive strain is found to be completely quenched, while the transition remains under the tensile strain albeit modified from the bulk behavior.
VO2 is a strongly correlated material, which undergoes a reversible metal insulator transition (MIT) coupled to a structural phase transition upon heating (T= 67{deg} C). Since its discovery the nature of the insulating state has long been debated and different solid-state mechanisms have been proposed to explain its nature: Mott-Hubbard correlation, Peierls distortion or a combination of both. Moreover, still now there is a lack of consensus on the interplay between the different degrees of freedom: charge, lattice, orbital and how they contribute to the MIT. In this manuscript we will investigate across the MIT the orbital evolution induced by a tensile strain applied to thin VO2 films. The strained films allowed to study the interplay between orbital and lattice degrees of freedom and to clarify MIT properties.
In the perovskite oxide SrCrO$_{3}$ the interplay between crystal structure, strain and orbital ordering enables a transition from a metallic to an insulating electronic structure under certain conditions. We identified a narrow window of oxygen partial pressure in which highly strained SrCrO$_{3}$ thin films can be grown using radio-frequency (RF) off-axis magnetron sputtering on three different substrates, (LaAlO$_{3}$)$_{0.3}$-(Sr$_{2}$TaAlO$_{6}$)$_{0.7}$ (LSAT), SrTiO$_{3}$ (STO) and DyScO$_{3}$ (DSO). X-ray diffraction and atomic force microscopy confirmed the quality of the films and a metal-insulator transition driven by the substrate induced strain was demonstrated.
We investigated the nature of transport and magnetic properties in SrIr0.5Ru0.5O3, (SIRO) which has characteristics intermediate between a correlated non-Fermi liquid state and an itinerant Fermi liquid state, by growing perovskite thin films on various substrates (SrTiO3 (001), (LaAlO3)0.3(Sr2TaAlO6)0.7 (001) and LaAlO3 (001)). We observed systematic variation of underlying substrate dependent metal-to-insulator transition temperatures at 80 K on SrTiO3, 90 K on (LaAlO3)0.3(Sr2TaAlO6)0.7 and 100 K on LaAlO3) in resistivity. Resistivity in the metallic region follows a T3/2 power law; whereas insulating nature at low T is due to the localization effect. Magnetoresistance (MR) measurement of SIRO on SrTiO3 (001) shows negative MR upto 25 K and positive MR above 25 K, with negative MR proportional to B1/2 and positive MR proportional to B2; consistent with the localized-to-normal transport crossover dynamics. Furthermore, observed spin glass like behavior of SIRO on SrTiO3 (001) in the localized regime, validates the hypothesis that (Anderson) localization favors glassy ordering. These remarkable features provide a promising approach for future applications and of fundamental interest in oxide thin films.
$V_2O_3$ has long been studied as a prototypical strongly correlated material. The difficulty in obtaining clean, well ordered surfaces, however, hindered the use of surface sensitive techniques to study its electronic structure. Here we show by mean of X-ray diffraction and electrical transport that thin films prepared by pulsed laser deposition can reproduce the functionality of bulk $V_2O_3$. The same films, when transferred in-situ, show an excellent surface quality as indicated by scanning tunnelling microscopy and low energy electron diffraction, representing a viable approach to study the metal-insulator transition (MIT) in $V_2O_3$ by means of angle-resolved photoemission spectroscopy. Combined, these two aspects pave the way for the use of $V_2O_3$ thin films in device-oriented heterostructures.
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