TY  - JOUR
AU  - Čermák, Petr
AU  - Schneidewind, Astrid
AU  - Liu, Benqiong
AU  - Koza, Michael Marek
AU  - Franz, Christian
AU  - Schönmann, Rudolf
AU  - Sobolev, Oleg
AU  - Pfleiderer, Christian
TI  - Magnetoelastic hybrid excitations in CeAuAl 3
JO  - Proceedings of the National Academy of Sciences of the United States of America
VL  - 116
IS  - 14
SN  - 1091-6490
CY  - Washington, DC
PB  - National Acad. of Sciences
M1  - FZJ-2019-02805
SP  - 6695 - 6700
PY  - 2019
AB  - 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.
LB  - PUB:(DE-HGF)16
C6  - pmid:30894488
UR  - <Go to ISI:>//WOS:000463069900036
DO  - DOI:10.1073/pnas.1819664116
UR  - https://juser.fz-juelich.de/record/862499
ER  -