Effect of Mn substitution by Ga on the optical properties of a metallic manganite

In a metallic manganite like La(2/3)Sr(1/3)MnO(3), the substitution of Mn(+3) by Ga(+3) dilutes the ferromagnetic order and locally cancels the Jahn-Teller distortion, without heavily affecting the crystal structure. One can thus follow the changes in the charge dynamics induced by Ga, until the ferro-metallic manganite is turned into an insulator. Here this phenomenon is studied in detail through the infrared reflectivity of five samples of La(2/3)Sr(1/3)Mn(1-x)Ga(x)O(3), with x increasing from 0 to 0.30 and for 50 < T < 320 K. A simple model which links the measured optical parameters to the magnetization M(x, T) well describes the behavior of the plasma frequency, the scattering rate, and the mid-infrared absorption along the metal-to-insulator transition.Comment: 8 pages including 7 figure

Spectrum of a magnetized strong-leg quantum spin ladder

Inelastic neutron scattering is used to measure the spin excitation spectrum of the Heisenberg $S=1/2$ ladder material (C$_7$H$_10$N)$_2$CuBr$_4$ in its entirety, both in the gapped spin-liquid and the magnetic field induced Tomonaga-Luttinger spin liquid regimes. A fundamental change of the spin dynamics is observed between these two regimes. DMRG calculations quantitatively reproduce and help understand the observed commensurate and incommensurate excitations. The results validate long-standing quantum field theoretical predictions, but also test the limits of that approach

Quasiparticle Breakdown and Spin Hamiltonian of the Frustrated Quantum Pyrochlore Yb2_2Ti2_2O7_7 in Magnetic Field

The frustrated pyrochlore magnet Yb$_2$Ti$_2$O$_7$ has the remarkable property that it orders magnetically, but has no propagating magnons over wide regions of the Brillouin zone. Here we use inelastic neutron scattering to follow how the spectrum evolves in cubic-axis magnetic fields. At high fields we observe in addition to dispersive magnons also a two-magnon continuum, which grows in intensity upon reducing the field and overlaps with the one-magnon states at intermediate fields leading to strong renormalization of the dispersion relations, and magnon decays. Using heat capacity measurements we find that the low and high field regions are smoothly connected with no sharp phase transition, with the spin gap increasing monotonically in field. Through fits to an extensive data set we re-evaluate the spin Hamiltonian finding dominant quantum exchange terms, which we propose are responsible for the anomalously strong fluctuations and quasiparticle breakdown effects observed at low fields.Comment: 5 pages main text + 19 pages supplemental materia

Observation of charge-density-wave excitations in manganites

In the optical conductivity of four different manganites with commensurate charge order (CO), strong peaks appear in the meV range below the ordering temperature T_{CO}. They are similar to those reported for one-dimensional charge density waves (CDW) and are assigned to pinned phasons. The peaks and their overtones allow one to obtain, for La{1-n/8}Ca{n/8}$MnO{3} with n = 5, 6, the electron-phonon coupling, the effective mass of the CO system, and its contribution to the dielectric constant. These results support a description of the CO in La-Ca manganites in terms of moderately weak-coupling and of the CDW theory.Comment: To be published on Phys. Rev. Let

Near-Field Tracking with Large Antenna Arrays: Fundamental Limits and Practical Algorithms

Applications towards 6G have brought a huge interest towards arrays with a high number of antennas and operating within the millimeter and sub-THz bandwidths for joint communication, sensing, and localization. With such large arrays, the plane wave approximation is often not accurate because the system may operate in the (radiating) near-field propagation region, namely the Fresnel region, where the electromagnetic field wavefront is spherical. In such a case, the curvature of arrival (CoA) is a measure of the spherical wavefront that can be used to infer the source position using only a single large antenna array. In this paper, we study a near-field tracking problem for inferring the position and the velocity of a moving source with an ad-hoc observation model that accounts for the phase-difference profile of a large receiving array. For this tracking problem, we derive the posterior Cramér-Rao Lower Bound (P-CRLB), and we provide insights on how the loss of positioning information outside the Fresnel region results from an increase of the ranging error rather than from inaccuracies of angular estimation. Then, we investigate the accuracy and complexity performance of different Bayesian tracking algorithms in the presence of model parameter mismatches and abrupt trajectory changes. Our results demonstrate the feasibility and high accuracy of most tracking approaches without the need for wideband signals and of any synchronization scheme

New provisions for the labelling of fishery and aquaculture products: Difficulties in the implementation of Regulation (EU) n. 1379/2013

The European Union (EU), within the renewal plan of the Common Fisheries Policy and the Common Market Organization, with the Cape IV of Reg. (EU) n. 1379/2013 have introduced new requirements for the labelling of fisheries and aquaculture products. These, as well as providing consumers with more complete information, integrate the provisions of Reg. (EU) n. 1169/2011 and acts as a tool to prevent frauds and illegal fishing. In this work the new seafood labelling provisions were evaluated, starting from the analysis of the art. 35 of the Chapter IV and comparing it with the previous EU dispositions (Reg. (EC) no. 104/2000 and no. 2065/2001). The exclusion of prepared and processed products and aquatic invertebrates from the application of the mandatory seafood labelling provisions and the role of the mass caterer operators with respect to the labelling requirements were identified as the two major shortcomings that still need to be better addressed by the legislator. Overall, what emerged from this work is that, if on the one hand the European legislation on seafood labelling has achieved important goals, evolving and improving itself, on the other it is still controversial and plagued by the same problems as 15 years ago. Therefore, the authors suggest that the regulation is modified at least extending its scope to all products and to at all stages of the fishery logistic chai

Exotic magnetism on the quasi-FCC lattices of the d3d^3 double perovskites La2_2NaB′'O6_6 (B′' == Ru, Os)

We find evidence for long-range and short-range ($\zeta$ $=$ 70 \AA~at 4 K) incommensurate magnetic order on the quasi-face-centered-cubic (FCC) lattices of the monoclinic double perovskites La$_2$NaRuO$_6$ and La$_2$NaOsO$_6$ respectively. Incommensurate magnetic order on the FCC lattice has not been predicted by mean field theory, but may arise via a delicate balance of inequivalent nearest neighbour and next nearest neighbour exchange interactions. In the Ru system with long-range order, inelastic neutron scattering also reveals a spin gap $\Delta$ $\sim$ 2.75 meV. Magnetic anisotropy is generally minimized in the more familiar octahedrally-coordinated $3d^3$ systems, so the large gap observed for La$_2$NaRuO$_6$ may result from the significantly enhanced value of spin-orbit coupling in this $4d^3$ material.Comment: 5 pages, 4 figure

Efficient Numerical Analysis of a Periodic Structure of Multistate Unit Cells

Application of the synthetic function expansion (SFX) algorithm to the analysis of active 1- and 2D periodic structures is presented. The single unit cell consisting of a microstrip line loaded by patches positioned below the line is turned into an active structure by inserting a pair of 2 switches to the two ends of each patch; the states of the pair of switches are changed contemporaneously. Variation of the states of the switches modifies the current distribution on the structure. The tunable multistate unit cell is arranged in 24-, 120-, and 9 × 24 element configurations and numerically analyzed. The computational complexity required for the characterization of the large number of possible configurations is lightened by the use of the proposed numerical method