title: Unusual diffusive effects on the ESR of Nd³⁺ ions in the tunable topologically nontrivial semimetal YBiPt.
abstract: Electron spin resonance (ESR) of diluted Nd(3+) ions in the topologically nontrivial semimetallic (TNSM) YBiPt compound is reported. The cubic YBiPt compound is a non-centrosymmetric half Heusler material which crystallizes in the F43m space group. The low temperature Nd(3+) ESR spectra showed a g-value of 2.66(4) corresponding to a Γ6 cubic crystal field Kramers' doublet ground state. Remarkably, the observed metallic and diffusive (Dysonian) Nd(3+) lineshape presented an unusual dependence with grain size, microwave power, Nd(3+) concentration and temperature. Moreover, the spin dynamic of the localized Nd(3+) ions in YBiPt was found to be characteristic of a phonon-bottleneck regime. It is claimed that, in this regime for YBiPt, phonons are responsible for mediating the diffusion of the microwave energy absorbed at resonance by the Nd(3+) ions to the thermal bath throughout the skin depth (δ ≃ μm). We argue that this is only possible because of the existence of highly mobile conduction electrons inside the skin depth of YBiPt that are strongly coupled to the phonons by spin-orbit coupling. Therefore, our unexpected ESR results point to a coexistence of metallic and insulating behaviors within the skin depth of YBiPt. This scenario is discussed in the light of the TNSM properties of this compound.
authors.affiliation: Instituto de Física 'Gleb Wataghin', UNICAMP, Campinas, SP 13083-859, Brazil.
authors.forename: G G
authors.initials: GG
authors.lastname: Lesseux
authors.forename: T M
authors.initials: TM
authors.lastname: Garitezi
authors.forename: P F S
authors.initials: PF
authors.lastname: Rosa
authors.forename: C B R
authors.initials: CB
authors.lastname: Jesus
authors.forename: S B
authors.initials: SB
authors.lastname: Oseroff
authors.forename: J L
authors.initials: JL
authors.lastname: Sarrao
authors.forename: Z
authors.initials: Z
authors.lastname: Fisk
authors.forename: R R
authors.initials: RR
authors.lastname: Urbano
authors.forename: P G
authors.initials: PG
authors.lastname: Pagliuso
authors.forename: C
authors.initials: C
authors.lastname: Rettori