Renormalization of the spin-wave spectrum in three-dimentional ferromagnets with dipolar interaction

Renormalization of the spin-wave spectrum is discussed in a cubic ferromagnet with dipolar forces at $T_C\gg T\ge0$. First 1/S-corrections are considered in detail to the bare spectrum $\epsilon_{\bf k} = \sqrt{Dk^2 (Dk^2 + S\omega_0\sin^2\theta_{\bf k})}$, where $D$ is the spin-wave stiffness, $\theta_{\bf k}$ is the angle between $\bf k$ and the magnetization and $\omega_0$ is the characteristic dipolar energy. In accordance with previous results we obtain the thermal renormalization of constants $D$ and $\omega_0$ in the expression for the bare spectrum. Besides, a number of previously unknown features are revealed. We observe terms which depend on azimuthal angle of the momentum $\bf k$. It is obtained an isotropic term proportional to $k$ which makes the spectrum linear rather than quadratic when $\sin\theta_{\bf k}=0$ and $k \ll \omega_0/D$. In particular a spin-wave gap proportional to $\sin\theta_{\bf k}$ is observed. Essentially, thermal contribution from the Hartree-Fock diagram to the isotropic correction as well as to the spin-wave gap are proportional to the demagnetizing factor in the direction of domain magnetization. This nontrivial behavior is attributed to the long-range nature of the dipolar interaction. It is shown that the gap screens infrared singularities of the first 1/S-corrections to the spin-wave stiffness and longitudinal dynamical spin susceptibility (LDSS) obtained before. We demonstrate that higher order 1/S-corrections to these quantities are small at $T\ll\omega_0$. However the analysis of the entire perturbation series is still required to derive the spectrum and LDSS when $T\gg\omega_0$.Comment: 11 pages, 1 figur

Quantum transitions from superfluid to insulating phases in disordered Bose systems

By the example of Heisenberg $d$-dimensional disordered antiferromagnets, we discuss quantum transitions at $d\ge2$ from magnetically ordered (superfluid) to various disordered (insulating) glassy phases (Bose-glass, Mott-glass, etc.) in Bose systems with quenched disorder. Our consideration is based on the hydrodynamic description of long-wavelength excitations and on the assumption that the ordered part of the system shows fractal properties near the transition point. We propose that the scaling ansatz for the free energy suggested before for the transition to the Bose-glass phase is applicable also for other transitions if the quenched disorder does not produce a local imbalance in sublattices magnetizations. We show using the scaling consideration that $\eta=2-z$ and $\beta=\nu d/2$, where $\eta$, $\beta$, and $\nu$, are critical exponents of the correlation function, the order parameter, and the correlation length, respectively, and $z$ is the dynamical critical index. These relations were missed in previous analytical discussions of Bose-glass and Mott-glass phases. They signify, in particular, that $z=d/2$ for the transition to the Mott-glass phase and that the density of states of localized excitations shows a superuniversal (i.e., independent of $d$) behavior near the transitions. Being derived solely from the scaling analysis, the above relations for $\eta$ and $\beta$ are valid also for the transition to the random-singlet phase.Comment: 10 pages, 1 figure. arXiv admin note: text overlap with arXiv:1701.0862

Magnon Bose condensation in symmetry breaking magnetic field

Magnon Bose condensation (BC)in the symmetry breaking magnetic field is a result of unusual form of the Zeeman energy, which has terms linear in the spin-wave operators and terms mixing excitations differ in the Wave-vector of the magnetic structure. The following examples are considered: simple easy-plane tetragonal antiferromagnets (AF), frustrated AF family$R_2Cu O_4$ where $R=Pr,Nd$ etc. and cubic magnets with the Dzyaloshinskii-Moriya interaction ($Mn Si$ etc.). In all cases the BC becomes important when the magnetic field becomes comparable with the spin-wave gap. The theory is illustrated by existing experimental results.Comment: Submitted to J. of Phys. Condens. Matter (Proceedings of International Conference "Highly Frustrated Magnets", Osaka (Japan), August 2006). 8 pages, 5 figure

Practical Strategies to Improve National Competitiveness

Today, the global community is faced with a new vision of the economy that aims to coordinate public policies with the purpose of ensuring sustainable growth to facilitate economic recovery under the current conditions and after the COVID-19 pandemic. The purpose of the study is to create a basic typology of strategies to improve national competitiveness in the context of globalization. The research methodology includes a comparison of economic development models and strategies for different countries around the world and an analysis of data from international organizations. The benchmarking of national strategies is based on the measurements’ evaluation for three groups of the GCI index components. The originality of the study stems from the fact that it proposed choosing a strategy for the development of the national economy with account taken of the level of its economic development. The strengths and weaknesses of competitiveness in the profile of the economy are identified and, whereby, a strategy to increase national competitiveness is chosen, according to the results of this analysis. The results of the study showed that the American model of economic development is the most competitive one among the examined models. In addition, the paper shows that the application of practical strategies for social integration, as well as mergers and acquisitions, will contribute to enhancing the national competitiveness in the context of economic growth and raising the living standards of the population. The findings of this research provide practical guidance for related professionals attempting to choose a suitable public policy to form effective and holistic national strategies and monitor the country’s progress over time. © The Author(s) 2021

Spin-wave interaction in two-dimensional ferromagnets with dipolar forces

We discuss the spin-wave interaction in two-dimensional (2D) Heisenberg ferromagnet (FM) with dipolar forces at $T_C\gg T\ge0$ using 1/S expansion. A comprehensive analysis is carried out of the first 1/S corrections to the spin-wave spectrum. In particular, similar to 3D FM discussed in our previous paper A.V. Syromyatnikov, PRB {\bf 74}, 014435 (2006), we obtain that the spin-wave interaction leads to the {\it gap} in the spectrum $\epsilon_{\bf k}$ renormalizing greatly the bare gapless spectrum at small momenta $k$. Expressions for the spin-wave damping $\Gamma_{\bf k}$ are derived self-consistently and it is concluded that magnons are well-defined quasi-particles in both quantum and classical 2D FMs at small $T$. We observe thermal enhancement of both $\Gamma_{\bf k}$ and $\Gamma_{\bf k}/\epsilon_{\bf k}$ at small momenta. In particular, a peak appears in $\Gamma_{\bf k}$ and $\Gamma_{\bf k}/\epsilon_{\bf k}$ at small $k$ and at any given direction of $\bf k$. If $S\sim1$ the height of the peak in $\Gamma_{\bf k}/\epsilon_{\bf k}$ is not larger than a value proportional to $T/D\ll1$, where $D$ is the spin-wave stiffness. In the case of large spins $S\gg1$ the peak in $\Gamma_{\bf k}/\epsilon_{\bf k}$ cannot be greater than that of the classical 2D FM found at $k=0$ which height is small only {\it numerically}: $\Gamma_{\bf 0}/\epsilon_{\bf 0}\approx0.16$ for the simple square lattice. Frustrating next-nearest-neighbor exchange coupling increases $\Gamma_{\bf 0}/\epsilon_{\bf 0}$ in classical 2D FM only slightly. We find expressions for spin Green's functions and the magnetization. The latter differs from the well-known result by S.V. Maleev, Sov. Phys. JETP {\bf 43}, 1240 (1976). The effect of the exchange anisotropy is also discussed briefly

Study of microbiome aberrations in patients with irritable bowel syndrome with diarrhea by next-generation sequencing

To investigate the microbiological composition of the intestines of patients with IBS-

Pinwheel VBS state and triplet excitations in the two-dimensional deformed kagome lattice

Determining ground states of correlated electron systems is fundamental to understanding novel phenomena in condensed matter physics. A difficulty, however, arises in a geometrically frustrated system in which the incompatibility between the global topology of an underlying lattice and local spin interactions gives rise to macroscopically degenerate ground states, potentially prompting the emergence of quantum spin states, such as resonating valence bond (RVB) and valence bond solid (VBS). Although theoretically proposed to exist in a kagome lattice -- one of the most highly frustrated lattices in two dimensions (2D) being comprised of corner-sharing triangles -- such quantum-fluctuation-induced states have not been observed experimentally. Here we report the first realization of the "pinwheel" VBS ground state in the S=1/2 deformed kagome lattice antiferromagnet Rb2Cu3SnF12. In this system, a lattice distortion breaks the translational symmetry of the ideal kagome lattice and stabilizes the VBS state.Comment: 10 pages, 4 figures and Supplemental Informatio

Evaluating the use of the Child and Adolescent Intellectual Disability Screening Questionnaire (CAIDS-Q) to estimate IQ in children with low intellectual ability

In situations where completing a full intellectual assessment is not possible or desirable the clinician or researcher may require an alternative means of accurately estimating intellectual functioning. There has been limited research in the use of proxy IQ measures in children with an intellectual disability or low IQ. The present study aimed to provide a means of converting total scores from a screening tool (the Child and Adolescent Intellectual Disability Screening Questionnaire: CAIDS-Q) to an estimated IQ. A series of linear regression analyses were conducted on data from 428 children and young people referred to clinical services, where FSIQ was predicted from CAIDS-Q total scores. Analyses were conducted for three age groups between ages 6 and 18 years. The study presents a conversion table for converting CAIDS-Q total scores to estimates of FSIQ, with corresponding 95% prediction intervals to allow the clinician or researcher to estimate FSIQ scores from CAIDS-Q total scores. It is emphasised that, while this conversion may offer a quick means of estimating intellectual functioning in children with a below average IQ, it should be used with caution, especially in children aged between 6 and 8 years old

Quantum magnetism in two dimensions: From semi-classical N\'eel order to magnetic disorder

This is a review of ground-state features of the s=1/2 Heisenberg antiferromagnet on two-dimensional lattices. A central issue is the interplay of lattice topology (e.g. coordination number, non-equivalent nearest-neighbor bonds, geometric frustration) and quantum fluctuations and their impact on possible long-range order. This article presents a unified summary of all 11 two-dimensional uniform Archimedean lattices which include e.g. the square, triangular and kagome lattice. We find that the ground state of the spin-1/2 Heisenberg antiferromagnet is likely to be semi-classically ordered in most cases. However, the interplay of geometric frustration and quantum fluctuations gives rise to a quantum paramagnetic ground state without semi-classical long-range order on two lattices which are precisely those among the 11 uniform Archimedean lattices with a highly degenerate ground state in the classical limit. The first one is the famous kagome lattice where many low-lying singlet excitations are known to arise in the spin gap. The second lattice is called star lattice and has a clear gap to all excitations. Modification of certain bonds leads to quantum phase transitions which are also discussed briefly. Furthermore, we discuss the magnetization process of the Heisenberg antiferromagnet on the 11 Archimedean lattices, focusing on anomalies like plateaus and a magnetization jump just below the saturation field. As an illustration we discuss the two-dimensional Shastry-Sutherland model which is used to describe SrCu2(BO3)2.Comment: This is now the complete 72-page preprint version of the 2004 review article. This version corrects two further typographic errors (three total with respect to the published version), see page 2 for detail