1,721,024 research outputs found
Universal signatures of the metamagnetic quantum critical endpoint: Application to CeRu2Si2
Full text linkA quantum critical endpoint related to a metamagnetic transition causes distinct signatures in the thermodynamic quantities of a compound. We argue that, irrespective of the microscopic details of the considered material, the diverging differential susceptibility combined with the Ising symmetry of the endpoint give rise to a number of characteristic metamagnetic phenomena. In the presence of a magnetoelastic coupling, one finds a correspondence of susceptibility, magnetostriction, and compressibility and, as a result, a pronounced crystal softening, a diverging Gruneisen parameter, a sign change of thermal expansion alpha(H), and a minimum in the specific-heat coefficient gamma(H). We illustrate these signatures and their relation on the metamagnetic crossover at 8 T in the prototypical heavy-fermion system CeRu2Si2.DFG [FOR 960, SFB 608]; Max-Planck Societ
Towards quantitative physics-informed device level models for organic light-emitting diodes
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Elastic Coupling at Quantum Phase Transitions and in Chiral Magnets
Full text linkWe investigate two topics in which elastic coupling to microscopic degrees of freedom shapes the physics on
large scales: Continuous phase transitions and chiral magnetism.
In the first part, we explore how elasticity influences the universal, critical behavior of classical and quantum phase transitions.
While the classical theory is well-established,
with lattice coupling leading to, depending on the thermodynamic ensemble, Fisher-renormalized critical exponents at constant volume or a first-order transition in the case of constant pressure,
quantum criticality coupled with elasticity presents different features.
Elastic coupling is non-perturbative if the critical exponent of specific heat is positive
and, in the quantum theory, induces microscopic instabilities.
We also investigate criticality in elastic ferroelectrics,
where coupling to shear strain leads to much richer physics for both classical and quantum phase transitions.
The second part focuses on chiral magnets, where inversion symmetry breaking gives rise to modulated spin textures such as helices and skyrmions,
which, when coupled to lattice degrees of freedom, induce modulated strain textures.
We investigate the effect of elastic coupling on chiral surface twists.
While magnetoelastic effects lead to surface strains and can modify twist profiles,
they fail to explain the large-scale surface reconstructions observed experimentally in the skyrmion phase
Single Molecule Spin valves
Full text linkTransport in the frame of the Landauer formalism for the single particle case is examined for carbon nanotubes decorated with magnetic molecules. Non-standard ab-initio calculations using constrained density functional theory to ensure the correct charge and magnetization densities are performed. Density functional calculations are performed on magnetic molecules in different spatial configurations: gas phase, crystal phase, and compound; the latter configuration type corresponds to a close-to-experiment system in which magnetic molecules are attached to a non-magnetic one. Based on the magnetization of the sitting molecules, two different magnetic states are examined. They are termed as antiparallel and parallel cases. They correspond to the experimental realizations shown elsewhere. The Kohn-Sham matrices, which are the result of the density functional simulations, are then used as an input for the transmission simulations which is performed using the Landauer formalism. Two transmission spectra are calculated corresponding to the alpha and beta spin channels per simulation. Differential conductance maps show a higher conductance for the parallel case compared to the antiparallel one for all the gate voltages where the conductance is different from zero. An empirical model is presented which mimics the real systems’ behaviour. It consists on a spin polarized tight-binding chain with two atoms per site where two defects are added to the central region simulating the real magnets. To model the CNT small bandgap, two orbitals per atom site were used. Similar results to those of the real system are calculated. It was found that the reason of the difference in conductance between one spin state and the other is that in the parallel case, the transmission for alpha and beta spin channels around the region of interest overlap giving a total transmission (which is the sum of both spins’ transmissions) larger to that of the antiparallel case where the alpha and beta transmissions are separated
Magnetic 2π Domain Walls for Tunable Majorana Devices
No full textTopological quantum computing aims to solve scaling and stability issues with current quantum computing platforms. Majorana bound states (MBSes) are a necessary ingredient for most proposals for topological quantum computing. Magnet-superconductor hybrids (MSHes) provide a promising platform for finding MBSes. We analyse the topology of MSHes with a magnetic 2π domain wall texture on the magnetic side and s-wave pairing and Rashba spin-orbit coupling (SOC) in the superconductor. The two layers are coupled with an antiferromagnetic exchange coupling. With this, we extend previous proposals concerning elongated skyrmions. We show that magnetic 2π domain walls are suitable for hosting MBSes and are advantageous compared to elongated skyrmions both for their attainability and mobility and for sidestepping issues with out-of-plane fields due to Pauli limiting. For various parameters of the system, we examine their influence on the topological phase space. Finally, we analyse the dynamics of the system under movement of the domain wall and show that MBSes can be moved in this way. This makes MSHes with magnetic 2π domain walls a suitable candidate for approachable and tunable Majorana devices
Variations on the Author
Full text link“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
Full text linkWe 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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