The dimer-RVB State of the Four-Leg Heisenberg Ladder: Interference among Resonances

We study the ground state of the 4-leg spin ladder using a dimer-RVB ansatz and the Lanczos method. Besides the well known resonance mechanism between valence bond configurations we find novel interference effects among nearby resonances.Comment: 4 pages, RevTex, 7 eps fig

Long-range Heisenberg models in quasi-periodically driven crystals of trapped ions

We introduce a theoretical scheme for the analog quantum simulation of long-range XYZ models using current trapped-ion technology. In order to achieve fully-tunable Heisenberg-type interactions, our proposal requires a state-dependent dipole force along a single vibrational axis, together with a combination of standard resonant and detuned carrier drivings. We discuss how this quantum simulator could explore the effect of long-range interactions on the phase diagram by combining an adiabatic protocol with the quasi-periodic drivings and test the validity of our scheme numerically. At the isotropic Heisenberg point, we show that the long-range Hamiltonian can be mapped onto a non-linear sigma model with a topological term that is responsible for its low-energy properties, and we benchmark our predictions with Matrix-Product-State numerical simulations.Comment: closer to published versio

Phase Diagram of the One Dimensional S=1/2S=1/2 XXZXXZ model with Ferromagnetic nearest-neighbor and Antiferromagnetic next-nearest neighbor interactions

We have studied the phase diagram of the one dimensional $S=1/2$ $XXZ$ model with ferromagnetic nearest-neighbor and antiferromagnetic next-nearest neighbor interactions. We have applied the quantum renormalization group (QRG) approach to get the stable fixed points and the running of coupling constants. The second order QRG has been implemented to get the self similar Hamiltonian. This model shows a rich phase diagram which consists of different phases which possess the quantum spin-fluid and dimer phases in addition to the classical N\'{e}el and ferromagnetic ones. The border between different phases has been shown as a projection onto two different planes in the phase space

Analysis of magnetic and structural properties in La0.6Sr 0.4MnO3 ferromagnetic particles under the influence of mechanical ball milling effect

We have investigated the magnetic, structural and morphological properties of La0.6Sr0.4MnO3 (LSMO-40) manganite particles, synthesized by solid state reaction method. The resulting LSMO-40 powders were milled in air atmosphere during 3, 6 and 12 hours, by using a planetary ball milling. Samples obtained were characterized by X-ray diffraction, scanning electron microscopy – SEM and magnetization measurements as a function of temperature and magnetic field. A Rietveld analysis was carried on each XRD pattern, and was observed a reduction in crystallite average size (Dv) with increased ball milling time, tM. This is associated with a decrease in particle size. A characteristic rhombohedral crystal structure for the LSMO-40 phase was identified (space group R3C), independent of the milling time of the powders. However, from SEM microstructure was observed more homogeneity in the grain distribution by milling process. The results of magnetic characterization, showed that samples with higher tM (smaller grain size), presented the lowest value of the saturation magnetization, which is attributed to surface effects that induce magnetically disordered states with decreasing particle sizes. This magnetic anisotropy surface is evidenced also on the changes of coercive fields, HC, measured at low temperatures, which increased with increasing tM