Breakdown of the strong multiplet description of the Sm2+ ion in the topological Kondo insulator SmB6: specific heat studies

• Published in: Scientific reports Vol. 9; no. 1; pp. 1 - 5
• Main Authors: Radwanski, Ryszard J., Nalecz, Dawid M., Ropka, Zofia
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 05.08.2019; Nature Publishing Group
• Subjects: 639/766/119/2792/4128; 639/766/119/995; Heat; Humanities and Social Sciences; Hybridization; multidisciplinary; Science; Science (multidisciplinary); Specific heat
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-019-47776-3

We have theoretically confirmed the existence of in-gap real quantum-mechanical states in SmB 6 , which have been suggested by experiments. These in-gap states, below the hybridization gap of 20 meV, are related to the Sm 2+ ion states and can be revealed by calculations within the spin-orbital | LSL z S z 〉 space, with L  = 3 and S  = 3. Our approach overcomes difficulties related to the singlet J  = 0 multiplet ground state. The in-gap states originate from the 49-fold degenerated term 7 F (4 f  6 ), which is split by cubic crystal-field (CEF) and spin-orbit (s − o) interactions. There is competition between these interactions: the six-order CEF interactions produce a 7-fold degenerated ground state, whereas the s − o interactions, even the weakest one, produce a singlet ( J  = 0) ground state. We have found preliminary CEF and s − o parameters that produce the lowest states at 0 K (singlet) and 91 K (triplet) and the next triplet at 221 K, i.e., within the hybridization gap. The derived states well explain the large extra specific heat of SmB 6 , confirming the consistency and adequateness of our theoretical approach with the breakdown of the strong multiplet description of the Sm 2+ ion in SmB 6 .