Crystalline Electric Field and Kondo Effect in SmOs4Sb12

Our ultrasound results obtained in pulsed magnetic fields show that the filled-skutterudite compound SmOs$_4$Sb$_{12}$ has the $\Gamma_{67}$ quartet crystalline-electric-field ground state. This fact suggests that the multipolar degrees of freedom of the $\Gamma_{67}$ quartet play an important role in the unusual physical properties of this material. On the other hand, the elastic response below $\approx$ 20 T cannot be explained using the localized 4$f$-electron model, which does not take into account the Kondo effect or ferromagnetic ordering. The analysis result suggests the presence of a Kondo-like screened state at low magnetic fields and its suppression at high magnetic fields above 20 T even at low temperatures.Comment: 4 pages, 4 figure

Γ3-type Lattice Instability and the Hidden Order of URu2Si2

We have performed ultrasonic measurements on single-crystalline URu2Si2 with pulsed magnetic fields, in order to check for possible lattice instabilities due to the hybridized state and the hidden-order state of this compound. The elastic constant (C11-C12)/2, which is associated with a response to the Γ3-type symmetry-breaking (orthorhombic) strain field, shows a three-step increase at H 35 T for H k c at low temperatures, where successive meta-magnetic transitions are observed in the magnetization. We discovered a new fact that the absolute change of the softening of (C11-C12)/2 in the temperature dependence is quantitatively recovered at the suppression of hybridized-electronic state and the hidden order in high-magnetic field for H k c associated with the successive transitions. The present results suggest that the Γ3-type lattice instability, is related to both the emergence of the hybridized electronic state and the hidden-order parameter of URu2Si2. On the other hand, magnetic fields H k [100] and [110] enhance the softening of (C11-C12)/2 in the hidden order phase, while no step-like anomaly is observed up to 68.7 T.We discuss the limitation of the localized-electron picture for describing these features of URu2Si2 by examination of a crystalline electric field model in terms of mean-field theory

Search for multipolar instability in URu2Si2 studied by ultrasonic measurements under pulsed magnetic field

The elastic properties of URu2Si2 in the high magnetic field region above 40 T, over a wide temperature range from 1.5 to 120 K, were systematically investigated by means of high-frequency ultrasonic measurements. The investigation was performed at high magnetic fields to better investigate the innate bare 5f-electron properties, since the unidentified electronic thermodynamic phase of unknown origin, the so-called "hidden order" (HO), and associated hybridization of conduction and f electrons (c-f hybridization) are suppressed at high magnetic fields. From the three different transverse modes we find contrasting results; both the Gamma(4)(B-2g) and Gamma(5)(E-g) symmetry modes C-66 and C-44 show elastic softening that is enhanced above 30 T, while the characteristic softening of the Gamma(3)(B-1g) symmetry mode (C-11 - C-12)/2 is suppressed in high magnetic fields. These results underscore the presence of a hybridization-driven Gamma(3)(B-1g) lattice instability in URu2Si2. However, the results from this work cannot be explained by using existing crystalline electric field schemes applied to the quadrupolar susceptibility in a local 5f(2) configuration. Instead, we present an analysis based on a band Jahn-Teller effect