Annamaria Kiss

Multipole Orders and Fluctuations in Strongly Correlated Electron Systems

In this paper we review experimental and theoretical results on higher electronic multipoles in solids with strong correlations. Recent experiments and their theoretical interpretation have confirmed the ordering of octupoles and even higher multipoles in rare-earth and actinide compounds with f electrons. The concept of multipoles is critically examined in point groups where spherical tensors of different ranks mix. Using a phenomenological approach, we demonstrate how linear and nonlinear couplings of different multipoles lead to rich phase diagrams and anomalies in physical observables. As actual representative systems, we first consider Ce x La 1- x B 6 , for which resonant X-ray scattering probed the octupole order for the first time, and NpO 2 , where quadrupoles induced by the octupole order have been observed. We then consider a class of compounds called skutterudites as the most convenient system for systematic study. Particular emphasis is placed on the ordering of scalar components from fourth-...

Scalar Order: Possible Candidate for Order Parameters in Skutterudites

Phenomenological Landau analysis shows that the properties of ordered phases in some skutterudites are consistently accounted for by a scalar-order parameter which preserves the cubic symmetry, even in the ordered phase. A universal value is found for the anisotropy ratio of the transition temperature in a magnetic field, homogeneous magnetization, and induced staggered magnetization. The difference in magnetic behavior between PrFe 4 P 12 and PrRu 4 P 12 near their phase transitions is explained within a single framework. For the low-field phase of PrFe 4 P 12 , the scalar order with Γ 1 g symmetry can explain (i) the absence of field-induced dipoles perpendicular to the magnetic field, (ii) isotropic magnetic susceptibility in the ordered phase, (iii) the field-angle dependence of the transition temperature, and (iv) the splitting pattern of the 31 P nuclear magnetic resonance (NMR) spectra. It is proposed how the order parameter in SmRu 4 P 12 is identified by NMR analysis of a single crystal.

Group theory and octupolar order in URu 2Si 2

Recent experiments on

On the Origin of Multiple Ordered Phases in PrFe4P12

\mathrm{U}{\mathrm{Ru}}_{2}{\mathrm{Si}}_{2}

Octupolar ordering of Γ 8 ions in a magnetic field

show that the low-pressure hidden order is nonmagnetic but it breaks time reversal invariance. Restricting our attention to local order parameters of

Hybridization Effects and Multipole Orders in Pr Skutterudites

5{f}^{2}

Phenomenological Theory of a Scalar Electronic Order : Application to Skutterudite PrFe4P12

shells, we find that the best candidate for hidden order is staggered order of either

Ordering and Crossover in a Pseudo-Sextet Localized Electron Model —Possible Scenario for SmRu4P12 Skutterudite—

{\mathcal{T}}_{z}^{\ensuremath{\beta}}

Sequence of multipolar transitions : Scenarios for URu2Si2

or

Theory of Successive Magnetic Transitions with Tilting of Moments–Application to NpFeGa5–

{\mathcal{T}}_{xyz}