Vienna University of Technology

About: Vienna University of Technology is a education organization based out in Vienna, Austria. It is known for research contribution in the topics: Laser & Context (language use). The organization has 16723 authors who have published 49341 publications receiving 1302168 citations.

Turning a nickelate Fermi surface into a cupratelike one through heterostructuring.

Abstract: Using the local density approximation and its combination with dynamical mean-field theory, we show that electronic correlations induce a single-sheet, cupratelike Fermi surface for hole-doped 1=1 LaNiO3=LaAlO3 heterostructures, even though both eg orbitals contribute to it. The Ni 3d 3z 2 � 1 orbital plays the role of the axial Cu 4s-like orbital in the cuprates. These two results indicate that ‘‘orbital engineering’’ by means of heterostructuring should be possible. As we also find strong antiferromagnetic correlations, the low-energy electronic and spin excitations in nickelate heterostructures resemble those of high-temperature cuprate superconductors. The discovery of high-temperature superconductivity (HTSC) in hole-doped cuprates [1] initiated the quest for finding related transition-metal oxides with comparable or even higher transition temperatures. In some systems, such as ruthenates [2] and cobaltates [3], superconductivity has been found. However, in these t2g systems superconductivity is very different from that in cuprates, and transition temperatures (Tc’s) are considerably lower. As it became possible to grow transition-metal oxides in heterostructures, this quest got a new direction: Novel effectively two-dimensional (2D) systems could be engineered. But which oxides, besides cuprates, are most promising for getting high Tc’s? The basic band structure of the hole-doped cuprates is that of a single 2D Cu 3d x 2 � y 2-like band which is less than half filled (configuration d 9� h ). In this situation, antiferromagnetic fluctuations prevail and are often believed to mediate the superconductivity. The Fermi surface (FS) from this x 2 � y 2 band has been observed in many overdoped cuprates and found to agree with the predictions of local density-functional (LDA) band theory. Recently the following idea for arriving at a cupratelike situation in nickelates was presented [4]: Bulk LaNiO3 (d 7 ) has one electron in two degenerate eg bands, but sandwiching a LaNiO3 layer between layers of an insulating oxide such as LaAlO3 will confine the 3z 2 � 1 orbital in the z direction and may remove this band from the Fermi level, thus leaving the electron in the x 2 � y 2 band. The possibility of finding bulk nickelates with an electronic structure analogous to that of cuprates was discarded awhile ago [5], but heterostructures offer new perspectives. Indeed, a major reconstruction of orbital states at oxide interfaces may recently have been observed [6], and this kind of phenomenon could lead to novel phases not present in the bulk. Extensive theoretical studies of mechanisms for orbital selection in correlated systems [7] have revealed the complexity of this problem, where details of the electronic structure and lattice distortions play decisive roles. It is therefore crucial to examine nickelate heterostructures by means of state-of-the-art theoretical methods and find the optimal conditions for x 2 � y 2 orbital selection. In this Letter we present results of electronic-structure calculations using the merger [8] of LDA band theory, which provides an ab initio description of the materials chemistry, and the dynamical mean-field theory (DMFT) [9], which includes electronic correlations. We find that the hopping between the x 2 � y 2 and 3z 2 � 1 orbitals substantially reduces the effects of correlations in the 3z 2 � 1 orbital. In this respect, eg electrons behave very differently than the t2g electrons, which have no interorbital hopping on a square lattice. Nevertheless, we do find that the correlations may sufficiently shift the bottom of the hybridizing e g bands relatively to each other to yield a FS with only one sheet. This sheet has predominantly x 2 � y 2 character and a shape like in the cuprates with the highest Tc max (Tc at optimum hole doping) [10], but even more extreme. Moreover, stretching the in-plane lattice constants by suitable choice of substrate reduces the correlation strength needed to produce a single-sheet FS. Since we also find strong antiferromagnetic fluctuations, somewhat larger than in the cuprates, nickelate heterostructures hold the basic ingredients for high-temperature superconductivity.

Recent advances in Wigner function approaches

Abstract: The Wigner function was formulated in 1932 by Eugene Paul Wigner, at a time when quantum mechanics was in its infancy. In doing so, he brought phase space representations into quantum mechanics. However, its unique nature also made it very interesting for classical approaches and for identifying the deviations from classical behavior and the entanglement that can occur in quantum systems. What stands out, though, is the feature to experimentally reconstruct the Wigner function, which provides far more information on the system than can be obtained by any other quantum approach. This feature is particularly important for the field of quantum information processing and quantum physics. However, the Wigner function finds wide-ranging use cases in other dominant and highly active fields as well, such as in quantum electronics—to model the electron transport, in quantum chemistry—to calculate the static and dynamical properties of many-body quantum systems, and in signal processing—to investigate waves passing through certain media. What is peculiar in recent years is a strong increase in applying it: Although originally formulated 86 years ago, only today the full potential of the Wigner function—both in ability and diversity—begins to surface. This review, as well as a growing, dedicated Wigner community, is a testament to this development and gives a broad and concise overview of recent advancements in different fields.

Light regulation of metabolic pathways in fungi.

Abstract: Light represents a major carrier of information in nature The molecular machineries translating its electromagnetic energy (photons) into the chemical language of cells transmit vital signals for adjustment of virtually every living organism to its habitat Fungi react to illumination in various ways, and we found that they initiate considerable adaptations in their metabolic pathways upon growth in light or after perception of a light pulse Alterations in response to light have predominantly been observed in carotenoid metabolism, polysaccharide and carbohydrate metabolism, fatty acid metabolism, nucleotide and nucleoside metabolism, and in regulation of production of secondary metabolites Transcription of genes is initiated within minutes, abundance and activity of metabolic enzymes are adjusted, and subsequently, levels of metabolites are altered to cope with the harmful effects of light or to prepare for reproduction, which is dependent on light in many cases This review aims to give an overview on metabolic pathways impacted by light and to illustrate the physiological significance of light for fungi We provide a basis for assessment whether a given metabolic pathway might be subject to regulation by light and how these properties can be exploited for improvement of biotechnological processes

Learning from interactive museum installations about interaction design for public settings

Abstract: This paper reports on the evaluation of a digitallyaugmented exhibition on the history of modern media. We discuss visitors' interaction with installations and corresponding interaction design issues, drawing on results from analysis of logfiles, interviews, and observation in the museum. We see this as an exploration into interaction design of interactive installations for public settings, using the evaluation as a case study on what makes an installation engaging and how it can provide an engaging experience for groups.

Experimental Test of Quantum Contextuality in Neutron Interferometry

Abstract: We performed an experimental test of the Kochen-Specker theorem based on an inequality derived from the Peres-Mermin proof, using spin-path (momentum) entanglement in a single neutron system. Following the strategy proposed by Cabello et al.[Phys. Rev. Lett. 100, 130404 (2008)], a Bell-like state was generated, and three expectation values were determined. The observed violation 2.291+-0.008not<=1 clearly shows that quantum mechanical predictions cannot be reproduced by noncontextual hidden-variable theories.