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Register a new userQuantifying electronic correlation strength in a complex oxide: a combined DMFT and ARPES study of LaNiO$_3$
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Elizabeth Nowadnick
Publication date
2015
fields
Physics
and research's language is
English
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The electronic correlation strength is a basic quantity that characterizes the physical properties of materials such as transition metal oxides. Determining correlation strengths requires both precise definitions and a careful comparison between experiment and theory. In this paper we define the correlation strength via the magnitude of the electron self-energy near the Fermi level. For the case of LaNiO$_3$, we obtain both the experimental and theoretical mass enhancements $m^star/m$ by considering high resolution angle-resolved photoemission spectroscopy (ARPES) measurements and density functional + dynamical mean field theory (DFT + DMFT) calculations. We use valence-band photoemission data to constrain the free parameters in the theory, and demonstrate a quantitative agreement between the experiment and theory when both the realistic crystal structure and strong electronic correlations are taken into account. These results provide a benchmark for the accuracy of the DFT+DMFT theoretical approach, and can serve as a test case when considering other complex materials. By establishing the level of accuracy of the theory, this work also will enable better quantitative predictions when engineering new emergent properties in nickelate heterostructures.
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The BaNi$_2$As$_2$ compound is investigated using both the angle-resolved photoemission spectroscopy (ARPES) in a wide binding energy range and combined computational scheme of local density approximation together with dynamical mean-field theory (LDA+DMFT). For more realistic comparison of LDA+DMFT spectral functions with ARPES data we take into account several experimental features: the photoemission cross-section, the experimental energy and angular resolutions and the photo-hole lifetime effects. In contrast to isostructural iron arsenides the BaNi$_2$As$_2$ within LDA+DMFT appears to be weakly correlated (effective mass enhancement about $1.2$). This dramatic reduction of the correlation strength comes from the increase of 3d-orbital filling, when going from Fe to Ni, together with rather large bare Ni-3d LDA bandwidth. Nevertheless, even weakened electron correlations cause remarkable reconstruction of the bare BaNi$_2$As$_2$ LDA band structure and corresponding LDA+DMFT calculations provide better agreement with ARPES than just renormalized LDA results.
Using the recently developed N-th order muffin-tin orbital-based downfolding technique in combination with the Dynamical Mean Field theory, we investigate the electronic properties of the much discussed Mott insulator TiOCl in the undimerized phase. Inclusion of correlation effects through this approach provides a description of the spectral function into an upper and a lower Hubbard band with broad valence states formed out of the orbitally polarized, lower Hubbard band. We find that these results are in good agreement with recent photo-emission spectra.
A combination of Density Functional Theory and the Dynamical Mean Field theory (DMFT) is used to calculate the magnetic susceptibility, heat capacity, and the temperature dependence of the valence band photoemission spectra. The continuous-time hybridization expansion quantum Monte-Carlo is utilized to provide the first approximation-free DMFT solution of emph{fcc} $delta$-Pu which includes the full rotationally-invariant exchange interaction. We predict that $delta$-Pu has a Pauli-like magnetic susceptibility near ambient temperature, as in experiment, indicating that electronic coherence causes the absence of local moments. Additionally, We show that volume expansion causes a crossover from incoherent to coherent electronic behavior at increasingly lower temperatures.
Variations in growth conditions associated with different deposition techniques can greatly affect the phase stability and defect structure of complex oxide heterostructures. We synthesized superlattices of the paramagnetic metal LaNiO3 and the large band gap insulator LaAlO3 by atomic layer-by-layer molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) and compared their crystallinity, microstructure as revealed by high-resolution transmission electron microscopy images and resistivity. The MBE samples show a higher density of stacking faults, but smoother interfaces and generally higher electrical conductivity. Our study identifies the opportunities and challenges of MBE and PLD growth and serves as a general guide for the choice of deposition technique for perovskite oxides.
The cobaltates have demonstrated a wide variety complex behavior. The Na rich region of the phase diagram displays various degrees of anomalous behavior, such as Curie-Weiss behavior near a band insulatorcite{Foo:2004}, charge disproportionationcite{Mukhamedshin:2005}, and non-Fermi-liquid behavior in the resistivitycite{Foo:2004}. Alternatively, the Na poor region of the phase diagram appears to be a Fermi-liquid. The magnetic susceptibility displays Pauli behavior, the resistivity is roughly quadratic at low temperaturescite{Foo:2004}, and the system appears to be homogeneouscite{Mukhamedshin:2005}. Therefore, the Na poor region of the phase diagram seems like a natural starting point to attempt to explain the ARPES experiments and heat capacity measurements from a quantitative standpoint.
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