University of Cambridge > > Quantum Matter Seminar > Inelastic neutron scattering and µSR investigations of an anisotropic hybridization gap in the Kondo insulators: CeT2Al10 (T=Fe, Ru and Os)

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

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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 (TN=27 K) and CeOs2Al10 (TN=28.5 K) and the Kondo insulating behaviour observed in the valence fluctuating compound CeFe2Al10 with a paramagnetic ground state down to 50 mK [1-6]. We are investigating this family of compounds using inelastic neutron scattering (INS) and µSR measurements 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 INS study as well as the existence of a spin gap above the magnetic ordering temperature in T=Ru and Os. Our INS studies on single crystals of CeRu2Al10 and CeOs2Al10 revealed dispersive gapped spin wave excitations below TN [6]. 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 [4-7]. I will discuss the origin of the anisotropic hybridization gap in CeFe2Al10 based on theoretical models of heavy-fermion semiconductors [8-10]. Further the effect of electron- and hole-doping as well as chemical pressure effect on the magnetic and transport properties of CeT2All0 compounds will be discussed based on our INS and µSR results [5]. Our µSR study reveals a long range magnetic ordering for electron doping in the Kondo insulator CeFe2Al10. I will compare the results of our INS study with that of topological Kondo insulators.

[1] A. M. Strydom, Physica B 404 , 2981 (2009). [2] Y. Muro et al, Phys. Rev. B 81 , 214401 (2010). [3] D.D. Khalyavin et al, Phys Rev. B 82 , 100405® (2010). [4] D.T. Adroja et al, Physica Scripta, 88, 068505, (2013). [5] D.T. Adroja et al, Phys Rev. B, 87, 224415 (2013); D.T. Adroja et al, Phys Rev. B 92 , 094425 (2015). [6] D.T. Adroja et al, Solid State Phenomena, 257, 11, (2016); arXiv:1607.06538v1 [7] J.M. Mignot et al, B 89 , 161103® (2014). [8] H. Ikeda and K. Miyake, J. Phys. Soc. Japan, 65, 1796 (1998). [9] P.S. Riseborough, J. Mag. Mag. Mat. 226-230, 127 (2001). [10] P.S. Riseborough and S.G.Magalhaes, J. Mag. Mag. Mat. 400, 3 (2016).

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