1,720,971 research outputs found
Identification of a Kitaev quantum spin liquid by magnetic field angle dependence
No full text© 2022, The Author(s).Quantum spin liquids realize massive entanglement and fractional quasiparticles from localized spins, proposed as an avenue for quantum science and technology. In particular, topological quantum computations are suggested in the non-abelian phase of Kitaev quantum spin liquid with Majorana fermions, and detection of Majorana fermions is one of the most outstanding problems in modern condensed matter physics. Here, we propose a concrete way to identify the non-abelian Kitaev quantum spin liquid by magnetic field angle dependence. Topologically protected critical lines exist on a plane of magnetic field angles, and their shapes are determined by microscopic spin interactions. A chirality operator plays a key role in demonstrating microscopic dependences of the critical lines. We also show that the chirality operator can be used to evaluate topological properties of the non-abelian Kitaev quantum spin liquid without relying on Majorana fermion descriptions. Experimental criteria for the non-abelian spin liquid state are provided for future experiments.11Nsciescopu
Interplay between spin-orbit coupling and Van Hove singularity in the Hund's metallicity of Sr2RuO4
No full text© 2020 American Physical Society. We investigate the roles of spin-orbit coupling and the Van Hove singularity in the dynamical properties of Sr2RuO4, which become prominent at zero and very low temperature, by means of density functional theory plus dynamical mean-field theory with an exact diagonalization solver. We examine the crossover between a Fermi liquid and a Hund's metal for a wide range of temperatures and Hund's coupling. In the absence of doping, we confirm that the Fermi liquid persists at zero temperature even with nonzero Hund's coupling. The freezing-moment mechanism suggests that thermal fluctuations lead to a suppression of the Fermi liquid phase and promote Hund's metallicity with incoherence. We show that the Van Hove singularity is an additional key ingredient to drive the suppression at very low temperature by observing a doping dependence of the freezing or long-lived paramagnetic moments. The role of spin-orbit coupling is marked by an amplified Van Vleck contribution of spin susceptibility, significantly promoting Hund's metallicity. Together with the known doping dependence of Hund's metallicity, the additional Van Hove singularity doping dependence found here may allow for the control of the Hund's metallicity of Sr2RuO4(t2g4) by a fine tuning of the doping or possibly even strain11sciescopu
Hund's metallicity enhanced by a van Hove singularity in cubic perovskite systems
No full text© 2021 American Physical Society.A van Hove singularity (VHS) often significantly amplifies the electronic instability of a crystalline solid, including correlation-induced phenomena such as Hund's metallicity. We perform a systematic study on the interplay between Hund's coupling and electronic structures with a VHS focusing on Hund's metallicity. We construct a simplified tight-binding model targeting cubic perovskite materials and test the effects of the VHS utilizing dynamical mean-field theory with an exact diagonalization solver. The quasiparticle weight and the low-frequency power exponent of the self-energy provide a quantitative estimation of metallicity over the phase diagram. We find the VHS to substantially enhance Hund's metallicity. The results here suggest a range of parameters through which a VHS can bring great synergy with Hund's coupling.11Nsciescopu
The stability of hole-doped antiferromagnetic state in a two-orbital model
Full text linkWe investigate the hole-doped antiferromagnetic state in a two-orbital model of cuprates. The
model also includes d3z2−r2 orbital. Unlike the one-orbital model, we find the antiferromagnetic
state stable against the hole doping for the cuprates with orbital splitting between dx2−y2 and d3z2−r2
orbitals being ∼1 eV. This results from the fact that the Hund’s coupling enforces the filling of
dx2−y2 orbital ≈1 indicated by a significant reduction of dx2−y2 spectral density at the Fermi level.
This, in turn, leads to the suppression of intraband fluctuations detrimental to the
antiferromagnetic phase. In this scenario, hole doping involves removal of mainly d3z2−r2 electrons
that are comparatively more localized. One important caveat of our meanfield theoretic result and
conclusion is that they are reliable only for a very low hole doping region.11Yscopu
Vestiges of Topological Phase Transitions in Kitaev Quantum Spin Liquids
Full text linkWe investigate signatures of topological quantum phase transitions (TQPTs) between the Z2 quantum spin liquids (QSLs). In two spatial dimensions, Z2 QSLs and their TQPTs are only well defined at zero temperature (T 1⁄4 0), and it is imperative to clarify their observable signatures under nonzero temperatures. Here, we present the vestiges of TQPTs between Z2 QSLs with Majorana fermions in terms of thermal Hall conductivity κxy at nonzero temperatures. The κxy=T shows characteristic temperature dependences around TQPTs. We argue that an exponential upturn near T 1⁄4 0 and the peak of κxy=T around massive excitation energy are observable smoking-gun signals of the TQPTs. Quantum critical fan-shape temperature dependences are uncovered across TQPTs. We also perform the parton mean-field analysis on a modified Kitaev model with next-nearest neighbor interactions finding TQPTs between the phases with different Chern numbers and their vestiges self-consistently. We discuss the implication of our results to the recent experiments in α-RuCl3. © 2019 American Physical Societ
Emergent localized states at the interface of a twofold PT -symmetric lattice
No full textⓒAmerican Physical Society. We consider the role of nontriviality resulting from a non-Hermitian Hamiltonian without band topology that conserves twofold PT symmetry assembled by interconnections between a PT -symmetric lattice and its timereversal partner. Twofold PT symmetry in the lattice produces additional surface exceptional points that play the role of new critical points, along with the bulk exceptional point. We show that there are two distinct regimes possessing symmetry-protected localized states of which localization lengths are robust against non-Hermiticity parameter. The states are demonstrated by numerical calculation of a quasi-one-dimensional ladder lattice and a two-dimensional bilayered square lattice.11Nscopu
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
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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