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[en] Many years and great effort have been spent constructing the microscopic model for the room temperature multiferroic BiFeO3. However, earlier models implicitly assumed that the cycloidal wavevector was confined to one of the three-fold symmetric axes in the hexagonal plane normal to the electric polarization. Because recent measurements indicate that can be rotated by a magnetic field, it is essential to properly treat the anisotropy that confines at low fields. We propose that the anisotropy energy confines the wavevectors to the three-fold axis and within the hexagonal plane with .
[en] We have carried out a high magnetic field study on single crystalline stoichiometric , a material discussed in terms quantum criticality in itinerant ferromagnets, by means of high field resistivity experiments. Our experiments have been performed at the Laboratoire National des Champs Magnétiques Intenses in Toulouse, France. The resistivity of single crystalline , has been investigated in external fields up to 15.5 T aligned along the c-axis in the temperature range of 1.4–55 K. The main focus of our study lies on the method to extract TN from the magnetoresistivity measurements, because TN could not be easily observed in temperature dependent resistivity for stoichiometric .
[en] In this article we present actual projects concerning high resolution measurements developed for future space missions based on ultracold atoms. This work involves the realization of a Bose Einstein Condensate in microgravitational environment and of an inertial atomic quantum sensor
[en] We consider the one-loop effective potential at zero and finite temperature in field theories with anisotropic space-time scaling, with critical exponent z=2, including both scalar and gauge fields. Depending on the relative strength of the coupling constants for the gauge and scalar interactions, we find that there is a symmetry breaking term induced at one loop at zero temperature and we find symmetry restoration through a first-order phase transition at high temperature.
[en] We performed 27Al-NMR measurements for the CaBe2Ge2 type single crystalline LaPd2Al2 in the temperature range from 100 K to 5 K to investigate the origin of the structural phase transition. We found that the line profile of the 27Al-NMR spectrum does not change entirely on passing through the structural phase transition at . Meanwhile, the peak position of the central line slightly change ( ppm) below 70 K, suggesting the orbital shift changes below . The present 27Al-NMR studies evidence that the local electronic state at Al site is hardly affected by the structural phase transition.
[en] Relative concentrations of six isomers of Ca at C74 are evaluated: one species with isolated pentagons, three isomers with a pentagon-pentagon junction, two structures with one pentagon-pentagon pair and one heptagon. The computations are carried out using the Gibbs energy in a broad temperature interval. It is shown that the endohedral species derived from the sole C74 cage with the isolated pentagons (D3h symmetry) prevails throughout. Two structures with a pentagon-pentagon junction come as minor isomers at high temperatures while the remaining three species are always negligible. For the dominant species, a kinetic barrier of less than 9 kcal/mol is computed for autoisomerizations mediated by motion of the encapsulated Ca atom
[en] Magnetic nanoparticles dispersed as a ferrofluid with volumetric concentrations in the range 0.4 to 10% and sizes ranging from 59-77 A have been studied via magnetic measurements at room and low temperatures. Remanence measurements have been used to determine switching and coupling effects. Particle size and concentration effects have been investigated and we find that the samples with higher concentrations have larger coercivities than expected due to coupling effects. Interactions have been found to be demagnetising overall as expected for dipolar interacting systems. Surface effects become evident below 10 K when thermal effects are weak
[en] Quantum Zeno effect is considered in parametric down-conversion with losses. In the optical region and for room temperatures quantum noise influences are not substantial for observation. Quantum losses in signal beam degrade the Zeno effect whereas they support it in the idler and compound beams
[en] Errors arising from the use of a sparse 63-station network in monitoring global and regional temperature changes are estimated by comparing results from a complete global data set from European Center for Medium Range forecasts analyses with those from the 63 gridpoints nearest the stations. For nine years of seasonal means, the correlations between the station network and the true values are generally quite high, but root-mean-square errors are also large outside of the tropics and are of the same order as the signal being sought. For the most part, this occurs because the variance of the 63-station network is too large so that although the overall low-frequency fluctuations are reasonably well depicted, their amplitude is too large. However, any missing data could greatly exacerbate errors arising from spatial sampling
[en] We construct an effective action for Polyakov loops using the eigenvalues of the Polyakov loops as the fun- damental variables. We assume Z(N) symmetry in the confined phase, a finite difference in energy densities between the confined and deconfined phases as T → 0, and a smooth connection to perturbation theory for large T. The low-temperature phase consists of N - 1 independent fields fluctuating around an explicitly Z(N) symmetric background. In the low-temperature phase, the effective action yields non-zero string tensions for all representations with non-trivial N-ality. Mixing occurs naturally between representations of the same N-ality. Sine-law scaling emerges as a special case, associated with nearest-neighbor interactions between Polyakov loop eigenvalues