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Accueil du site > Evènements du laboratoire > Séminaires > Archives - Séminaires 2013 > Recent ultrasound measurements on strongly correlated electron systems under magnetic field and hydrostatic pressure in Japan and HZDR Dresden

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Recent ultrasound measurements on strongly correlated electron systems under magnetic field and hydrostatic pressure in Japan and HZDR Dresden

26/11/2013, Yoshiki Nakanishi (Graduate School of Engineering, Iwate University, Japan and Dresden HMLF, HZDR, Germany)

A role of electric quadrupolar degrees of freedom on the low temperature properties in the vicinity of quantum critical point (QCP) is a subject of increasing interest in recent years. Ultrasound investigation is one of the most powerful method to probe the phononic degrees of freedom including the electric quadrupolar ones and possible lattice instabilities in 4f-electron systems. Indeed, it is an ideal experimental tool to investigate the degeneracy of electric quadrupolar degrees of freedom and its dynamics. In this talk, we will show some of our recent results obtained both in Iwate University, Japan and Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Germany. The series of compounds RTr2Al20 (R = rare earth, Tr = Ti, V, and Cr), which belongs to a new heavy fermion system, crystallize in the cubic CeCr2Al20-type structure with the space group Fd-3m, where the R atoms are coordinated by the Frank-Kasper cages formed by 16 zinc atoms.[1] This near spherical distribution of neighboring Al atoms gives rise to the possible low crystalline electric field (CEF) split levels and also leads to a relatively isolated ionic state of the R atoms. Thus, a low-lying degenerated levels derived from 4f - multiplets ground state e.g. the degeneracy of electric quadrupolar degrees of freedom is highly expected in those systems. Furthermore, their cage structure possibly leads to anharmonic vibrations of a guest ion (R) in an oversized cage and effectively strong hybridization between localized 4f electrons and conduction ones owing to the large number of the cage Al atom to the guest ion in these systems. We will show the high-field properties of PrV2Al20, in particular its elastic property of the novel high-field phase discovered recently. Furthermore, we will show ultrasonic investigations of an antiferromagnet CeRh2Si2 under hydrostatic pressure. CeRh2Si2 with the tetragonal ThCr2Si2-type structure exhibits a successive magnetic phase transition at TN1 = 36 K and TN2 = 25 K at ambient pressure. [2, 3] A clear elastic softening toward TN1 emerges and grows gradually with increasing P as a function of temperature. Surprisingly, the largest elastic softening was finally observed under around Pc, where a superconductivity appears. These experimental results suggest an importance of the 4f ground state property of Ce ion, possibly leading to an intermediate charge state of Ce. We discuss the possible origin and scenario of the phenomena observed in the both systems.

 

[1] A. Sakai et. al. : J. Phys. Soc. Jpn. 80 063701 (2011).
[2] B. Chevalier et al, : J. Phys. C 3 1847 (1991).
[3] S. Araki et al, : J. Phys. : Condens. Matter 14 L377 (2002).