Revisiting the Possible 4f⁷ 5d¹ Ground State of Gd Impurities in SmB₆ by Electron Spin Resonance

Abstract

The search for topological states in strongly correlated electron systems has renewed the interest in the Kondo insulator SmB6. One of the most intriguing previous results was an anomalous electron spin resonance spectrum in Gd-doped SmB6. This spectrum was attributed to Gd 2+ ions because it could be very well decribed by a model considering a change in the valence from Gd 3+ to Gd 2+ , a dynamic Jahn-Teller effect and a 4f 7 5d 1 ground state in the Hamiltonian. In our work, we have revisited this scenario using electron spin resonance and energy dispersive X-ray spectroscopy measurements. Our results suggest that the resonance is produced by Gd 2+ ions; however the resonance stems from an extrinsic oxide impurity phase that lies on the surface of the crystal.

Bulk and surface properties of SmB6

“…Wiese et al argue for a divalent 4 f 7 5d 1 configuration for Gd owing to a trapped conduction electron. These experiments have been also revisited recently by Souza et al, and the origin of the unusual Gd 2+ -like signal is found to be an oxide impurity phase on the surface of the crystal [186]. In the very dilute limit, the low-temperature fine structure of the Gd 3+ electron spin resonance spectra follows the expected cubic crystal-field environment.…”