Lattice effects in singlet ground state systems

Abstract

The influence of phonons on Singlet Ground State dynamics is studied. Three systems were investigated: 1) TbP: Here a softening of the c44‐mode above TN is observed, which can be quantitatively explained as an induced cooperative Jahn–Teller effect. 2) PrSn3: In this system the elastic constants show little temperature dependance for T≳TN=7.3°K despite the fact that the Γ5 level is only about 9°k above Γ1. We observe a 4% softening in the c44 mode. 3) Pr3X4 with X=S, Se, Te: X‐ray and elastic constant measurments revealed a structural transition above TC for X=S, Se. In Pr3Se4 TC=13°K, Ta=40°K. This is not of the coop. J‐T type because at Ta=62°K. These structural transitions are probably induced by similar mechanisms as those occuring in other metal alloys (e.g. In‐Tl). Pr3Te4 exhibits no structural transition, but very strong magnetic field dependent effects. Although all these systems exhibit interesting features (phonon softening and structural instabilities), there is no apparent strong coupling between the elastic waves and the soft magnetic mode. The reason is that that they couple different crystal field levels (Γ1−Γ3, Γ1−Γ5 for phonons and Γ1−Γ4 for magnetic excitations in cubic symmetry). A full report will be published elsewhere.