Using inelastic neutron scattering, we map a 14 meV coherent resonant mode in the topological Kondo insulator SmB6 and describe its relation to the low energy insulating band structure. The resonant intensity is confined to the X and R high symmetry points, repeating outside the first Brillouin zone and dispersing less than 2 meV, with a 5d-like magnetic form factor. We present a slave-boson treatment of the Anderson Hamiltonian with a third neighbor dominated hybridized band structure. This approach produces a spin exciton below the charge gap with features that are consistent with the observed neutron scattering. We find that maxima in the wave vector dependence of the inelastic neutron scattering indicate band inversion.PACS numbers: 71.10. Li, 71.27.+a, 75.30.Mb Recent theoretical work suggests SmB 6 could be a topological Kondo insulator (TKI), with an insulating bulk at low temperatures and a topologically protected metallic surface [1][2][3][4][5][6][7] that was previously ascribed to impurities [8]. Because strong electron-electron interactions produce the insulating state, the surface may support exotic correlated physics [9][10][11].Experimental investigations [12][13][14][15][16][17][18], particularly spinresolved angle-resolved photo-emission spectroscopy (ARPES) [19], have provided compelling evidence that SmB 6 is a TKI. However, information about the band structure within ≈ 50 meV of the Fermi level is limited due to the polar surface, multiplet structure, and strong correlations. In this energy range the magnetic neutron scattering is sensitive to the renormalized band structure through the imaginary part of the momentum (Q) and energy ( ω) dependent generalized susceptibility.In this Letter, we present a comprehensive measurement of the inelastic magnetic neutron scattering cross section covering the full Brillouin zone of SmB 6 for energies below 50 meV. We pair our experimental results with a slave-boson treatment of an Anderson Hamiltonian, and discuss how pseudonesting conditions for the renormalized band structure can be examined to corroborate a topologically nontrivial band structure for SmB 6 . The low energy magnetic neutron scattering cross section for SmB 6 is dominated by a resonant mode near 14 meV with bandwidth < 2 meV. Previous publications reported intensity at R [ ( 1 2 1 2 1 2 )], and investigated it versus temperature and doping [20][21][22][23][24][25]. Here, we show the mode is also intense near the X [( 1 2 00)] point and present, albeit dramatically weaker, beyond the first zone. Through this mulitzone mapping, we provide evidence for an anomalous 5d form factor for the weakly dispersing mode, and develop a minimal band structure based on dominant third neighbor hopping. The hybridized tight-binding model goes beyond early two-band theoretical treatments [26,27] by allowing f -electron fluctuations as appropriate for a mixed valence compound and provides a link between the wave vector dependence of the magnetic neutron scattering and band inversion in Kondo insu...

The paramagnetic response of mixed-valence samarium hexaboride has been studied by inelastic neutron scattering using a low-absorption double-isotope single crystal of 154Sm11 B6. Measurements were performed for energy transfers 0

Samarium hexaboride (SmB6) is a Kondo insulator, with a narrow gap due to hybridization between localized and conduction electrons. Despite being an insulator, many samples show metal-like properties. Rare-earth purification is exceedingly difficult, and nominally pure samples may contain 2% or more of impurities. Here to determine the effects of rare-earth doping on SmB6, we synthesized and probed a series of gadolinium-doped samples. We found a relationship between specific heat and impurity moment screening which scales systematically. Consistent with this finding, our neutron scattering experiments of a high purity sample of doubly isotopic 154Sm11B6 show no intrinsic excitations below the well-established 13 meV spin-exciton. The result of introducing impurities into a Kondo insulator is incompletely understood, but it is clear from our measurements that there is a systematic relationship between rare-earth impurities and metal-like properties in SmB6.