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Seminar: Petr Čermák

  • Petr Čermák: Magnetoelastic hybrid excitations in non-centrosymmetric heavy fermion compound CeAuAl3
  • 18. 1. 2017, 14:30
  • lecture room F2, first floor Ke Karlovu 5
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Abstract:

Hybridized excitations that comprise of well-understood collective modes have received increasing interest as the possible origin of unconventional materials properties and novel functionalities. In strongly correlated electron systems the effects of electron-phonon interactions are typically neglected, being deemed not important for an overall understanding. However, recently neutron time-of-flight spectroscopy on polycrystalline CeCuAl3 have provided putative evidence for a vibron, i.e., a combined crystal field – optical phonon excitation [1], whereas no such excitation could be detected in the isostructural sister compound CeAuAl­3 [2]. This raises the question to what extent such hybrid modes represent a generic property of the series of CeTAl3 compounds (T: transition metal element) or even f-electron systems in general. To pursue this question, we have revisited the properties of CeAuAl3 using triple axis neutron spectroscopy on a float-zoned high-quality single-crystal. In contrast with early conjectures, we find two pieces of strong evidence suggesting strong crystal field – phonon interactions and the formation of a novel hybrid mode. First, at the zone center there is clearly a hybridized excitation between the crystal-field and phonons, which appears to be in general agreement with vibronic bound state reported for CeCuAl3 [1]. Second, we observe a distinct anticrossing of the transverse acoustic phonon with the Γ7(1) crystal field level. To the best of our knowledge such an anti-crossing has not been reported before. Both phenomena are in agreement with observed dominant phonon scattering processes by the localized 4f electrons [3]. Taken together, our results suggest that strongly hybridized crystal field – phonon excitations may, in fact, be rather common in f-electron compounds.

[1] D.T. Adroja, et al., Phys. Rev. Lett. 108, 216402 (2012).

[2] D.T. Adroja, et al., Phys. Rev. B 91, 134425 (2015).

[3] Y. Aoki, et al., Phys. Rev. B 62, 87 (2000).