A Schwinger-boson approach to the kagome with Dzyaloshinskii-Moriya interactions: phase diagram and dynamical structure factors

We have obtained the zero-temperature phase diagram of the kagome antiferromagnet with Dzyaloshinskii-Moriya interactions in Schwinger-boson mean-field theory. We find quantum phase transitions (first or second order) between different topological spin liquids and Neel ordered phases (either the $\sqrt{3} \times \sqrt{3}$ state or the so-called Q=0 state). In the regime of small Schwinger-boson density, the results bear some resemblances with exact diagonalization results and we briefly discuss some issues of the mean-field treatment. We calculate the equal-time structure factor (and its angular average to allow for a direct comparison with experiments on powder samples), which extends earlier work on the classical kagome to the quantum regime. We also discuss the dynamical structure factors of the topological spin liquid and the Neel ordered phase.Comment: 8 pages, 9 figure

Finite-temperature phase transitions in S = 1/2 three-dimensional Heisenberg magnets from high-temperature series expansions

Many frustrated spin models on three-dimensional (3D) lattices are currently being investigated, both experimentally and theoretically, and develop new types of long-range orders in their respective phase diagrams. They present finite-temperature phase transitions, most likely in the Heisenberg 3D universality class. However, the combination between the 3D character and frustration makes them hard to study. We present here several methods derived from high-temperature series expansions (HTSEs), which give exact coefficients directly in the thermodynamic limit up to a certain order; for several 3D lattices, supplementary orders than in previous literature are reported for the HTSEs. We introduce an interpolation method able to describe thermodynamic quantities at T>Tc, which we use here to reconstruct the magnetic susceptibility and the specific heat and to extract universal and nonuniversal quantities (for example, critical exponents, temperature, energy, entropy, and other parameters related to the phase transition). While the susceptibility associated with the order parameter is not usually known for more exotic long-range orders, the specific heat is indicative of a phase transition for any kind of symmetry breaking. We present examples of applications on ferromagnetic and antiferromagnetic models on various 3D lattices and benchmark our results whenever possible

Chirality and Z2Z_2 vortices in an Heisenberg spin model on the kagom\'e lattice

The phase diagram of the classical \jj model on the \kag lattice is investigated using extensive \mc simulations. In a realistic range of parameters, this model has a low-temperature chiral-ordered phase without long-range spin order. We show that the critical transition marking the destruction of chiral order is preempted by the first order proliferation of \Zdeux point defects. The core energy of these vortices appears to vanish when approaching the T=0 phase boundary, where both \Zdeux defects and gapless magnons contribute to disordering the system at very low temperature. This situation might be typical of a large class of frustrated magnets. Possible relevance for real materials is also discussed.Comment: 4 pages, 4 figure

Lattice symmetries and regular states in classical frustrated antiferromagnets

We consider some classical and frustrated lattice spin models with global O(3) spin symmetry. There is no general analytical method to find a ground-state if the spin dependence of the Hamiltonian is more than quadratic (i.e. beyond the Heisenberg model) and/or if the lattice has more than one site per unit cell. To deal with these situations, we introduce a family of variational spin configurations, dubbed "regular states", which respect all the lattice symmetries modulo global O(3) spin transformations (rotations and/or spin flips). The construction of these states is explicited through a group theoretical approach, and all the regular states on the square, triangular, honeycomb and kagome lattices are listed. Their equal time structure factors and powder-averages are shown for comparison with experiments. All the well known N\'eel states with 2 or 3 sublattices appear amongst regular states on various lattices, but the regular states also encompass exotic non-planar states with cubic, tetrahedral or cuboctahedral geometry of the T=0 order parameter. Whatever the details of the Hamiltonian (with the same symmetry group), a large fraction of these regular states are energetically stationary with respect to small deviations of the spins. In fact these regular states appear as exact ground-states in a very large range of parameter space of the simplest models that we have been looking at. As examples, we display the variational phase diagrams of the J1-J2-J3 Heisenberg model on all the previous lattices as well as that of the J1-J2-K ring-exchange model on square and triangular lattices.Comment: 15 pages, 12 figures, 1 tabl

Non-linear magnons and exchange Hamiltonians of delafossite proximate quantum spin liquids

Quantum spin liquids (QSL) are theoretical states of matter with long-range entanglement and exotic quasiparticles. However, they generally elude quantitative theory, rendering their underlying phases mysterious and hampering efforts to identify experimental QSL states. Here we study triangular lattice resonating valence bond QSL candidate materials KYbSe$_2$ and NaYbSe$_2$. We measure the magnon modes in their 1/3 plateau phase, where quantitative theory is tractable, using inelastic neutron scattering and fit them using nonlinear spin wave theory. We also fit the KYbSe$_2$ heat capacity using high temperature series expansion. Both KYbSe$_2$ fits yield the same magnetic Hamiltonian to within uncertainty, confirming previous estimates and showing the Heisenberg $J_2/J_1$ to be an accurate model for these materials. Most importantly, comparing KYbSe$_2$ and NaYbSe$_2$ shows that smaller $A$-site Na$^+$ ion has a larger $J_2/J_1$ ratio. However, hydrostatic pressure applied to KYbSe$_2$ increases the ordering temperature (a result consistent with density functional theory calculations), indicating that pressure decreases $J_2/J_1$. These results show how periodic table and hydrostatic pressure can tune the $A$YbSe$_2$ materials in a controlled way.Comment: 7 pages, 7 figures; 4 pages and 7 additional figures of supplemental informatio

Magnetic crystals and helical liquids in alkaline-earth fermionic gases

The joint action of a synthetic gauge potential and of atomic contact repulsion in a one-dimensional alkaline-earth(-like) fermionic gas with nuclear spin I leads to the existence of a hierarchy of fractional insulating and conducting states with intriguing properties. We unveil the existence and the features of those phases by means of both analytical bosonization techniques and numerical methods based on the density-matrix renormalization group algorithm. In particular, we show that the gapless phases can support helical modes, whereas the gapped states, which appear under certain conditions, are characterised both by density and magnetic order. Several distinct features emerge solely for spin I larger than 1/2, thus making their study with cold-atoms unique. We will finally argue that these states are related to the properties of an unconventional fractional quantum Hall effect in the thin-torus limit. The properties of this hierarchy of states can be experimentally studied in state-of-the-art cold-atom laboratories

Diez años

Es deber de todo jurista, de todo iusfilósofo, de todo ciudadano, bregar por la plena vigencia del derecho y por la observación de las normas. Y no sólo eso; es preciso, además, pensar mentalmente las normas jurídicas y pensarlas luego verbalmente, para que su formulación oral o escrita sean la genuina expresión de lo pensado. La sociedad humana debe responder a la naturaleza racional del hombre en su organización y en su funcionamiento. A su turno, la razón es esclava de sus formas y éstas se nos evidencian cuando la ciencia de la Lógica las pone de manifiesto. Toda ciencia, todo conocimiento, no sólo es adquirido y pensado sino que es comunicado y, en esa expresión, se deben observar también las reglas que nuestra condición humana exige.Dos enclaves de justicia en la Ilíada / Ariel Álvarez Gardiol – El imaginario social y la independencia judicial / Armando S. Andruet (h) – Principio de igualdad. Opciones que plantea la solución de casos / Jorge Augusto Barbará – Derecho y dialéctica / Julio César Castiglione – A propósito del “control de convencionalidad” / Raúl E. Fernández – Aproximaciones al control de logicidad / Olsen A. Ghirardi – Un modelo de juez democrático / Rolando Oscar Guadagna – El derecho ante el enfoque analítico / Ricardo A. Guibourg – Los entimemas forenses y su validez en la fundamentación sentencial / María del Pilar Hiruela de Fernández – El derecho y la feminización del fenómeno laboral / Patricia Elena Messio – Derecho, política y valoraciones / Carlos Enrique Pettoruti – Un test filosófico a la teoría del conflicto de derechos / Marina Andrea Riba – La vigencia de Nimio de Anquín / Luis Roberto Rueda – La declinación del derecho. Ontología. Ontología del derecho / Héctor Hugo Segura – Le dédoublement du sujet: entre sujet juridique et sujet social / Jean-Marc Trigeaud – Los derechos humanos y la actividad jurisdiccional interpretativa / Rodolfo L. Vigo –publishedVersionÁlvarez Gardiol, Ariel. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Andruet (h), Armando S. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Barbará, Jorge Augusto. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Castiglione, Julio César. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Fernández, Raúl E.. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Ghirardi, Olsen A. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Guadagna, Rolando Oscar. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Guibourg, Ricardo A. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Hiruela de Fernández, María del Pilar. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Messio, Patricia Elena. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Pettoruti, Carlos Enrique. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Riba, Marina Andrea. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Rueda, Luis Roberto. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Segura, Héctor Hugo. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Trigeaud, Jean-Marc. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina.Vigo, Rodolfo L. Academia Nacional de Derecho y Ciencias Sociales de Córdoba; Argentina

Logarithmic divergent specific heat from high-temperature series expansions: Application to the two-dimensional XXZ Heisenberg model

International audienceWe present an interpolation method for the specific heat c v (T), when there is a phase transition with a logarithmic singularity in c v at a critical temperature T = T c. The method uses the fact that c v is constrained both by its high temperature series expansion and just above T c by the type of singularity. We test our method on the ferro-and antiferromagnetic Ising models on the two-dimensional square, triangular, honeycomb, and kagome lattices, where we find an excellent agreement with the exact solutions. We then explore the XXZ Heisenberg model, for which no exact results are available

Experimental observation using particle image velocimetry of inertial waves in a rotating fluid

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