Metal-insulator transition in oxygen-deficient<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">LaNiO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn><mml:mi mathvariant="normal">−</mml:mi><mml:mi mathvariant="italic">x</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>perovskites

Sánchez, R.D.; Causa, M.T.; Caneiro, A.; Butera, A.; Vallet‐Regí, María; Sayagués, María Jesús; Gonzalez-Calbet, J. M.; García-Sanz, F.; Rivas, J.

doi:10.1103/physrevb.54.16574

Phys. Rev. B

1996

DOI: 10.1103/physrevb.54.16574

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Metal-insulator transition in oxygen-deficientLaNiO3−xperovskites

R.D. Sánchez

M.T. Causa

A. Caneiro

et al.

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Cited by 128 publications

(82 citation statements)

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“…For this conducting state, interactions between spins of the Ni 2+ atoms are expected to be of the RKKY type such that, in the presence of disorder -recall that the system is close to a MI transition-they may promote a spin-glass type of ordering. We note that in bulk LNO samples, for large enough densities of vacancies, spin glass behavior has indeed been reported [6,7]. In 2D, a true spin-glass transition would only take place at T = 0 K [20], and one does not expect the kind of static and time dependent anomalies that are the hallmark of this state.…”

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confidence: 99%

“…This material has also been reported to be sensitive to the degree of disorder. For instance, increasing the amount of oxygen vacancies can lead to weak localization and metal-insulator (MI) transitions, as well as antiferromagnetic ordering and spin glass behaviour [6][7][8]. LNO based heterostructures have been grown and transport measurements have revealed a MI transition as the LNO thickness is reduced to only a few unit cells (u.c.)…”

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Metal-Insulator Transition in UltrathinLaNiO3Films

et al. 2011

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Transport in ultrathin films of LaNiO3 evolves from a metallic to a strongly localized character as the film's thickness is reduced and the sheet resistance reaches a value close to h/e 2 , the quantum of resistance in two dimensions. In the intermediate regime, quantum corrections to the Drude lowtemperature conductivity are observed; they are accurately described by weak localization theory. Remarkably, the negative magnetoresistance in this regime is isotropic, which points to magnetic scattering associated with the proximity of the system to either a spin glass state or the charge ordered antiferromagnetic state observed in other rare earth nickelates.Complex oxides are exciting materials in which the interplay between charge, spin, orbital and lattice degrees of freedom leads to a wealth of novel and exotic phenomena. Among these materials, LaNiO 3 (LNO), a metal and paramagnet lacking any ordering phenomena in bulk [1][2][3], has recently become the subject of intense research. This was mainly triggered by theoretical work [4] which suggested the possibility of orbital ordering and high-T c superconductivity in superlattices where very thin LNO layers are separated by insulating layers, confining the conduction to two dimensions (2D). These predictions have yet to be confirmed experimentally. LNO bulk and thin films have been extensively studied in the past, showing a large effective mass and enhanced Pauli paramagnetism, which has been attributed to strong correlations [1,2,5]. This material has also been reported to be sensitive to the degree of disorder. For instance, increasing the amount of oxygen vacancies can lead to weak localization and metal-insulator (MI) transitions, as well as antiferromagnetic ordering and spin glass behaviour [6][7][8]. LNO based heterostructures have been grown and transport measurements have revealed a MI transition as the LNO thickness is reduced to only a few unit cells (u.c.) [9,10]. This behaviour is in agreement with the MI transition observed in single ultrathin LNO films [11]. Understanding the nature of transport for this compound in the ultrathin limit appears essential for future investigation of LNO-based heterostructures and serves as the motivation for this work. Upon reduction of the LNO thickness, transport evolves from a metallic to a strongly localized behavior as the room temperature sheet resistance approaches h/e 2 ∼ 25 kΩ, the quantum of resistance in 2D. We find a transition region between the metallic and the strongly localized states where the films show an upturn in the resistivity at low temperatures which can be explained by the theory of weak localization. Surprisingly, the magnetoresistance (MR) is found to be isotropic in this regime. We attribute this to the presence of magnetic scattering and discuss its possible origins. Films were grown on (001) SrTiO 3 substrates by off-axis rf magnetron sputtering, leading to fully strained epi-

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Metal-Insulator Transition in UltrathinLaNiO3Films

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“…Conductivity of bulk LNO has been shown to be sensitive to oxygen deficiency which tightly correlates with Ni valence [14]. To clarify if Ni 2+ is connected to oxygen deficiency, we annealed the SLs at 900 o C in flowing ultra-pure O 2 at 1 Atm for 12 hours.…”

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Effect of polar discontinuity on the growth of LaNiO3/LaAlO3 superlattices

Liu

Kareev

Prosandeev

et al. 2010

Applied Physics Letters

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We have conducted a detailed microscopic investigation of [LaNiO3(1 u.c.)/LaAlO3(1 u.c.)]N superlattices grown on (001) SrTiO3 and LaAlO3 to explore the influence of polar mismatch on the resulting electronic and structural properties. Our data demonstrate that the initial growth on the non-polar SrTiO3 surface leads to a rough morphology and unusual 2+ valence of Ni in the first LaNiO3 layer, which is not observed after growth on the polar surface of LaAlO3. A newly devised model suggests that the polar mismatch can be resolved if the perovskite layers grow with an excess of LaO, which also accounts for the observed electronic, chemical, and structural effects.Recently complex oxide ultra-thin films have been drawing enormous attention due to the possibility of stabilizing unusual quantum phases and building interface-controlled devices [1,2]. Towards this goal, the problem of polar interfaces is of fundamental importance, since a polar crystal structure grown on a non-polar substrate would be unstable due to the depolarizing fields [3,4]. To avoid this issue, some mechanism must set in to compensate the potential jump by forcing electronic, structural or chemical (nonstoichiometry) changes. In particular, the active work on the LaAlO 3 /SrTiO 3 system [5][6][7] has suggested an electron transfer between atomic layers that decreases Ti valence by 0.5 at the expense of 0.5e charge in the terminating atomic plane. Additionally, an alloy effect has been observed at the interface [8], and first-principles computations revealed a contribution of ionic displacements [9].In this letter, we report on the microscopic observation of an unusual valence state of Ni 2+ in ultrathin LaNiO 3 /LaAlO 3 superlattices (SL) grown on non-polar (or weakly polar) (001) TiO 2 -terminated SrTiO 3 (STO) substrates. This is in marked contrast to identical SLs grown on polar LaAlO 3 (LAO), which always exhibit the 3+ valence of the bulk-like LaNiO 3 (LNO). To clarify the origin of these phenomena, we have tracked the changes of the Ni valence as a function of the SL thickness and developed an experimental procedure to monitor and control the electronic state of a transition metal ion.High-quality epitaxial LNO/LAO SLs were grown on (001) TiO 2 -terminated STO single crystal substrates by pulsed laser deposition with in situ monitoring by RHEED [10]. To minimize induced defects, STO substrates were prepared by our recently developed chemical wet-etch procedure ('Arkansas treatment') [11]. A complementary set of SLs were also grown on LAO single crystal substrates. Detailed spectroscopic information was acquired in the soft x-ray regime in both fluorescence yield (FY) mode and total electron yield (TEY) mode at the Ni L 3,2 absorption edge at the 4ID-C beamline of the Advanced Photon Source, ANL. To obtain precise information on the Ni charge state, all spectra were aligned by simultaneously measuring a NiO (Ni 2+ ) standard with the SLs. Synchrotron-based x-ray diffraction has confirmed the high structural quality and the full epitaxy of t...

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“…[2][3][4][5][6][7][8][9][10][11] The use of aggressive reducing agents, such as Ca 2 H, 12 has enabled the realization of ABO 2 compounds such as SrFeO 2 and LaNiO 2 via topotactic transformations from as-grown ABO 3 and ABO 2.5 films. 13,14 Given the sensitive coupling between δ and physical properties, [15][16][17] topotactic oxidation and reduction reactions have been used to induce large changes to the electronic, optical, and magnetic properties of epitaxial films [18][19][20] and may prove applicable in ionically controlled solid state devices. [21][22][23][24] A second class of topotactic reaction involves the insertion or substitution of a different anion on the oxygen site to stabilize mixed-anion perovskites such as oxyfluorides.…”

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Comparison of topotactic fluorination methods for complex oxide films

et al. 2015

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Metal-insulator transition in oxygen-deficientLaNiO3−xperovskites

Cited by 128 publications

References 24 publications

Metal-Insulator Transition in UltrathinLaNiO3Films

Metal-Insulator Transition in UltrathinLaNiO3Films

Effect of polar discontinuity on the growth of LaNiO3/LaAlO3 superlattices

Comparison of topotactic fluorination methods for complex oxide films

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