Correlated topological insulators: spectroscopic investigations combined with band structure calculations.
Final Report Abstract
The putatively topological non-trivial Kondo semimetal CeRu4Sn6 and Kondo insulator SmB6 have been investigated with x-ray spectroscopic methods. The ground-state symmetries and ff –excitations have been determined with NIXS and RIXS, the valence with hard x-ray photoelectron spectroscopy. An 8% contribution of the f0 configuration in the ground state qualifies CeRu4Sn6 as a weak topological insulator according to Large-N mean field theory results. The ff excitations as determined with RIXS give credit to DFT+DMFT results that found a |Jz=1/2;J=5/2> ground state symmetry with some |Jz=1/2,J=7/2> admixture of the higher multiplet and with hybridization-induced mixing in of the |Jz=3/2,J=5/2>. In SmB6 we identified the Γ8 quartet as the crystal-field ground state which governs the topological properties of SmB6, thus giving guidance to follow-up calculations. They should be performed within a reduced basis of only Γ8 states for the construction of a low-energy many-body Hamiltonian. Our findings agree with the anticlockwise spin texture as observed in spin-resolved APRES predicted by theory for a Γ8 ground state. Note, for a Γ7 the spin directions should be reversed. However, our finding of a Γ8 local ground-state symmetry contradicts the outcome of several density functional band structure calculations. We confirmed the Γ8 ground state with RIXS. With RIXS, we were further able to give an upper and lower limit for the crystal-field splitting of the Sm3+ ground-state multiple, namely 10 meV ≤ ∆CF6H5/2 ≤30 meV .
Publications
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Ce 3p hard x-ray photoelectron spectroscopy study of the topological Kondo insulator CeRu4Sn6, J. of Phys. Conf. Series 807, 022001 (2017)
M. Sundermann, K. Chen, Y. Utsumi, Y.-H. Wu, K.-D. Tsuei, J. Haenel, A. Prokofiev, S. Paschen, A. Tanaka, L.H. Tjeng, A. Severing
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The quartet ground state in CeB6: an inelastic x-ray scattering study, Euro Phys. Lett. 117, 17003 (2017)
M. Sundermann, K. Chen, H. Yavas, Han-Oh Lee, Z. Fisk, M. W. Haverkort, L. H. Tjeng, A.Severing
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4f Crystal Field Ground State of the Strongly Correlated Topological Insulator SmB6, Phys. Rev. Lett. 120, 016402 (2018)
M. Sundermann, H. Yavaş, K. Chen, D. J. Kim, Z. Fisk, D. Kasinathan, M. W. Haverkort, P. Thalmeier, A. Severing, L. H. Tjeng
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Determining the local low-energy excitations in the Kondo semimetal CeRu4Sn6 using resonant inelastic x-ray scattering, Phys. Rev B 98, 081116 (R) (2018)
A. Amorese, K. Kummer, N. Brookes, O. Stockert, D.T. Adroja, A. Strydom, A. Sidorenko, H. Winkler, D. A. Zocco, A. Prokofiev, S. Paschen, M.W. Haverkort, L.H. Tjeng, A. Severing
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Resonant inelastic x-ray scattering investigation of the crystal-field splitting of Sm3+ in SmB6, Phys. Rev. B 100, 241107(R) (2019)
A. Amorese, O. Stockert, K. Kummer, N. B. Brookes, D.-J. Kim, Z. Fisk, M. W. Haverkort, P. Thalmeier, Liu Hao Tjeng, A. Severing
