Electronic superlattice revealed by resonant scattering from random impurities in Sr3Ru2O7.

Resonant elastic x-ray scattering (REXS) is an exquisite element-sensitive tool for the study of subtle charge, orbital, and spin superlattice orders driven by the valence electrons, which therefore escape detection in conventional x-ray diffraction (XRD). Although the power of REXS has been demonstrated by numerous studies of complex oxides performed in the soft x-ray regime, the cross section and photon wavelength of the material-specific elemental absorption edges ultimately set the limit to the smallest superlattice amplitude and periodicity one can probe. Here we show--with simulations and REXS on Mn-substituted Sr3Ru2O7--that these limitations can be overcome by performing resonant scattering experiments at the absorption edge of a suitably-chosen, dilute impurity. This establishes that--in analogy with impurity-based methods used in electron-spin-resonance, nuclear-magnetic resonance, and Mössbauer spectroscopy--randomly distributed impurities can serve as a non-invasive, but now momentum-dependent probe, greatly extending the applicability of resonant x-ray scattering techniques.

Crystal-field level inversion in lightly Mn-doped Sr3Ru2O7.

Sr3(Ru(1-x)Mnx)2O7, in which 4d-Ru is substituted by the more localized 3d-Mn, is studied by x-ray dichroism and spin-resolved density functional theory. We find that Mn impurities do not exhibit the same 4+ valence of Ru, but act as 3+ acceptors; the extra eg electron occupies the in-plane 3d(x2-y2) orbital instead of the expected out-of-plane 3d(3z2-r2). We propose that the 3d-4d interplay, via the ligand oxygen orbitals, is responsible for this crystal-field level inversion and the material's transition to an antiferromagnetic, possibly orbitally ordered, low-temperature state.

Local tunneling spectroscopy across a metamagnetic critical point in the bilayer ruthenate Sr3Ru2O7.

The local spectroscopic signatures of metamagnetic criticality in Sr(3)Ru(2)O(7) were explored using scanning tunneling microscopy (STM). Singular features in the tunneling spectrum were found close to the Fermi level, as would be expected in a Stoner picture of itinerant electron metamagnetism. These features showed a pronounced magnetic field dependence across the metamagnetic critical point, which cannot be understood in terms of a naive Stoner theory. In addition, a pseudogap structure was observed over several tens of meV, accompanied by a c(2 x 2) superstructure in STM images. This result represents a new electronic ordering at the surface in the absence of any measurable surface reconstruction.

Imaging nanoscale electronic inhomogeneity in the lightly doped Mott insulator Ca(2-x)NaxCuO2Cl2.

The spatial variation of electronic states was imaged in the lightly doped Mott insulator Ca(2-x)NaxCuO2Cl2 using scanning tunneling microscopy or spectroscopy. We observed nanoscale domains with a high local density of states within an insulating background. The observed domains have a characteristic length scale of 2 nm (approximately 4-5a, a: lattice constant) with preferred orientations along the tetragonal [100] direction. We argue that such spatially inhomogeneous electronic states are inherent to slightly doped Mott insulators and play an important role for the insulator to metal transition.

Interposed bone grafts to accommodate endosteal implants for retaining mandibular overdentures. A 1-7 year follow-up study.

The results are reported on 34 edentulous patients, who underwent interposed autogenous bone graft augmentation in the symphysis of the mandible, combined with bone-hydroxylapatite onlay augmentation of the area posterior to the mental foramina. Two to four implants were placed in the grafted symphysis after 3-5 months. An overdenture was constructed three months later. The follow-up period ranged from one to seven years. An average loss of mandibular bone height of 10-13% was observed. The data provided no evidence of a further time-dependent resorption from two-and-half to seven years.

Juvenile xanthogranuloma of the tongue.

Oral juvenile xanthogranuloma is a rare condition, with only 10 histologically proven cases previously described. A histologically unusual variant is reported here, diagnosis of which was aided by the use of immunohistochemical stains. Previously reported cases are reviewed, and their characteristics are tabulated and discussed.