%0 Journal Article
%A Čermák, Petr
%A Schneidewind, Astrid
%A Liu, Benqiong
%A Koza, Michael Marek
%A Franz, Christian
%A Schönmann, Rudolf
%A Sobolev, Oleg
%A Pfleiderer, Christian
%T Magnetoelastic hybrid excitations in CeAuAl 3
%J Proceedings of the National Academy of Sciences of the United States of America
%V 116
%N 14
%@ 1091-6490
%C Washington, DC
%I National Acad. of Sciences
%M FZJ-2019-02805
%P 6695 - 6700
%D 2019
%X Nearly a century of research has established the Born–Oppenheimer approximation as a cornerstone of condensed-matter systems, stating that the motion of the atomic nuclei and electrons may be treated separately. Interactions beyond the Born–Oppenheimer approximation are at the heart of magneto-elastic functionalities and instabilities. We report comprehensive neutron spectroscopy and ab initio phonon calculations of the coupling between phonons, CEF-split localized 4f electron states, and conduction electrons in the paramagnetic regime of CeAuAl3, an archetypal Kondo lattice compound. We identify two distinct magneto-elastic hybrid excitations that form even though all coupling constants are small. First, we find a CEF–phonon bound state reminiscent of the vibronic bound state (VBS) observed in other materials. However, in contrast to an abundance of optical phonons, so far believed to be essential for a VBS, the VBS in CeAuAl3 arises from a comparatively low density of states of acoustic phonons. Second, we find a pronounced anticrossing of the CEF excitations with acoustic phonons at zero magnetic field not observed before. Remarkably, both magneto-elastic excitations are well developed despite considerable damping of the CEFs that arises dominantly by the conduction electrons. Taking together the weak coupling with the simultaneous existence of a distinct VBS and anticrossing in the same material in the presence of damping suggests strongly that similarly well-developed magneto-elastic hybrid excitations must be abundant in a wide range of materials. In turn, our study of the excitation spectra of CeAuAl3 identifies a tractable point of reference in the search for magneto-elastic functionalities and instabilities.
%F PUB:(DE-HGF)16
%9 Journal Article
%$ pmid:30894488
%U <Go to ISI:>//WOS:000463069900036
%R 10.1073/pnas.1819664116
%U https://juser.fz-juelich.de/record/862499