Abstract
9Be NMR measurements have been performed for a single crystal UBe13 with Tc≈0.86 K. For an applied field parallel to [001] direction, we observed a well-split 9Be NMR line with the sharp line-width of ≈10 Oe, guaranteeing the high-quality of the single crystal from the microscopic viewpoint. We also calculated the electric field gradient (9EFG) tensor at Be(II) site using the band-structure calculation based on an FLAPW-LDA method. From the field-angle dependence of 9Be-NMR spectra together with the result of the band-structure calculation, we identified the 9EFG and 9Be Knight shift tensors. The Knight shift of UBe13 is enhanced by a factor of hundreds compared to that of a pure Be metal, suggesting the local spin density at Be 2s and 2p orbitals is enhanced through the hybridization with 5f electrons. The isotropic and anisotropic hyperfine fields are obtained as Aiso≈436 Oe/μB, (As1,As2,As3)≈(192,44,−236) Oe/μB. The anisotropic part can be explained by the spin-dipolar field attributed to the local-spin-density at Be 2p orbital, and the 2p orbital perpendicular to the mirror plane [for example 2px for Be(IIA)] contributes mainly to the conduction band. On the other hand, the isotropic part mainly originates from the core polarization hyperfine field of the Be s shell due to the unpaired Be 2p electrons. The present results give direct evidence that the Be 2p orbital is responsible for conduction bands.
