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Control of orbital reconstruction in (LaAlO3)M/(SrTiO3)N(001) quantum wells by strain and confinement
No full textControl of orbital reconstruction in (LaAlO3)/(SrTiO3)(001) quantum wells by strain and confinement
No full textThe diverse functionality emerging at oxide interfaces calls for a fundamental understanding of the mechanisms and control parameters of electronic reconstructions. Here, we explore the evolution of electronic phases in (LaAlO3)(M)/(SrTiO3)(N) (001) superlattices as a function of strain and confinement of the SrTiO3 quantum well. Density functional theory calculations including a Hubbard U term reveal a charge ordered Ti3+ and Ti4+ state for N = 2 with an unanticipated orbital reconstruction, displaying alternating d(xz) and d(yz) character at the Ti3+ sites, unlike the previously reported d(xy) state, obtained only for reduced c-parameter at a(STO). At a(LAO) c-compression leads to a Dimer-Mott insulator with alternating d(xz), d(yz) sites and an almost zero band gap. Beyond a critical thickness of N = 3 (a(STO)) and N = 4 (a(LAO)) an insulator-to-metal transition takes place, where the extra e/2 electron at the interface is redistributed throughout the STO slab with a d(xy) interface orbital occupation and a mixed d(xz) + d(yz) occupation in the inner layers. Chemical variation of the SrTiO3 counterpart (LaAlO3 vs. NdGaO3) proves that the significant octahedral tilts and distortions in the SrTiO3 quantum well are induced primarily by the electrostatic doping at the polar interface and not by variation of the SrTiO3 counterpart
Tuning of the carrier localization, magnetic and thermoelectric properties in ultrathin (LaNiO)/(LaAlO)(001) superlattices by oxygen vacancies
Get PDFUsing a combination of density functional theory calculations with an on-site
Coulomb repulsion term (DFT+) and Boltzmann transport theory within the
constant relaxation time approximation, we explore the effect of oxygen
vacancies on the electronic, magnetic, and thermoelectric properties in
ultrathin (LaNiO)/(LaAlO)(001) superlattices (SLs).
For the pristine SL, an antiferromagnetic charge-disproportionated (AFM-CD)
({})() phase is stabilized,
irrespective of strain. At = 0.125 and 0.25, the localization of
electrons released from the oxygen defects in the NiO plane triggers a
charge-disproportionation, leading to a ferrimagnetic insulator both at
(tensile strain) and (compressive
strain). At = 0.5, an insulating phase emerges with alternating
stripes of Ni (high-spin) and Ni (low-spin) and oxygen vacancies
ordered along the [110] direction (S-AFM), irrespective of strain. This results
in a robust -type in-plane power factor of 24~W/K cm at
and 14~W/K cm at at 300~K
(assuming relaxation time ~fs). Additionally, the pristine and
= 0.5 SLs are shown to be dynamically stable. This demonstrates the
fine tunability of electronic, magnetic, and thermoelectric properties of
ultrathin nickelate superlattices by oxygen vacancies.Comment: 7 pages, 3 figure
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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