SPring-8, the large synchrotron radiation facility

Speaker : Dr Devashibhai Adroja

Language : English

Affiliation : ISIS Facility, Rutherford Appleton Laboratory

Title : Inelastic neutron scattering investigations of an anisotropic hybridization gap in the Kondo insulators: CeT₂Al₁₀ (T=Fe, Ru and Os)

Abstract:
The recent discovery of topological Kondo insulating behaviour in strongly correlated electron systems has generated considerable interest in Kondo insulators both experimentally and theoretically. The Kondo semiconductors CeT₂Al₁₀ (T=Fe, Ru and Os) possessing a c-f hybridization gap have received considerable attention recently because of the unexpected high magnetic ordering temperature of CeRu₂Al₁₀ (T_N=27 K) and CeOs₂Al₁₀ (T_N=28.5 K) and the Kondo insulating behaviour observed in the valence fluctuating compound CeFe₂Al₁₀ with a paramagnetic ground state down to 50 mK [1-3]. We are investigating this family of compounds, both in polycrystalline and single crystal form, using inelastic neutron scattering to understand the role of anisotropic c-f hybridization on the spin gap formation as well as on their magnetic properties. We have observed a clear sign of a spin gap in all three compounds from our polycrystalline study as well as the existence of a spin gap above the magnetic ordering temperature in T=Ru and Os. Our inelastic neutron scattering studies on single crystals of CeRu₂Al₁₀ and CeOs₂Al₁₀ revealed dispersive gapped spin wave excitations below T_N. Analysis of the spin wave spectrum reveals the presence of strong anisotropic exchange, along the c-axis (or z-axis) stronger than in the ab-plane. These anisotropic exchange interactions force the magnetic moment to align along the c-axis, competing with the single ion crystal field anisotropy, which prefers moments along the a-axis. In the paramagnetic state (below 50 K) of the Kondo insulator CeFe₂Al₁₀, we have also observed dispersive gapped magnetic excitations which transform into quasi-elastic scattering on heating to 100 K [4-5]. We will discuss the origin of the anisotropic hybridization gap in CeFe₂Al₁₀ based on theoretical models of heavy-fermion semiconductors [6-8]. Further the effect of electron- and hole-doping as well as chemical pressure effect on the magnetic and transport properties of CeT₂Al_l0 compounds will be discussed. We will compare the observation of spin and charge gap formation in CeT₂Al₁₀ with that observed in Ce-based Skutterudite compounds as well as that of topological Kondo insulators.

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[3] D.T. Adroja et al, Physica Scripta, 88, 068505, (2013).
[4] D.T. Adroja et al, Phys Rev. B, 87, 224415 (2013).
[5] J.M. Mignot et al. B 89, 161103(R) (2014).
[6] H. Ikeda and K. Miyake, J. Phys. Soc. Japan, 65, 1796 (1998).
[7] P.S. Riseborough, J. Mag. Mag. Mat. 226-230, 127 (2001).
[8] P.S. Riseborough and S.G.Magalhaes, J. Mag. Mag. Mat. 400, 3 (2016).

Organizer : Satoshi Tsutsui
Mail : satoshi@spring8.or.jp
PHS : 3479