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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• Dr. Adroja Devashibhai, ISIS Facility, Rutherford Appleton Laboratory
• Wednesday 07 March 2018, 11:15-12:30
• Mott Seminar Room (531), Cavendish Laboratory, Department of Physics.

If you have a question about this talk, please contact Romy Hall.

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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