The Sn͞Ge(111) interface has been investigated across the 3 3 3 ! p 3 3 p 3 R30 ± phase transition using core level and valence band photoemission spectroscopies. We find, both above and below the transition, two different components in the Sn 4d core level and a band splitting in the surface state crossing the Fermi energy. Theoretical calculations show that these two effects are due to the existence of two structurally different kinds of Sn atoms that fluctuate at room temperature between two positions and are stabilized in a 3 3 3 structure at low temperature. [S0031-9007(98)

Possible magnetic skyrmion device applications motivate the search for structures that extend the stability of skyrmion spin textures to ambient temperature. Here, we demonstrate an experimental approach to stabilize a room temperature skyrmion ground state in chiral magnetic films via exchange coupling across non-magnetic spacer layers. Using spin polarized low-energy electron microscopy to measure all three Cartesian components of the magnetization vector, we image the spin textures in Fe/Ni films. We show how tuning the thickness of a copper spacer layer between chiral Fe/Ni films and perpendicularly magnetized Ni layers permits stabilization of a chiral stripe phase, a skyrmion phase, and a single domain phase. This strategy to stabilize skyrmion ground states can be extended to other magnetic thin film systems and may be useful for designing skyrmion based spintronics devices. V C 2015 AIP Publishing LLC. [http://dx.

The Cu(111) surface state has been mapped for vicinal surfaces with variable step densities by angleresolved photoemission. Using tunable synchrotron radiation to vary the k dependence perpendicular to the surface, as well as the k k dependence, we find a switch between two qualitatively different regimes at a miscut of 7 ± (17 Å terrace width). For larger miscut angles the step modulation of the wave function dominates, and for smaller miscut angles the terrace modulation dominates. These observations resolve an apparent inconsistency between prior photoemission and STM results.

STM images show that vicinal Au(788) surfaces are made up of a uniform array of (111)-oriented terraces of similar width ͑ϳ3.8 nm͒. This uniformity makes it possible to study the electronic structure of the resulting step superlattice by angle-resolved photoemission. We show that for this terrace array the surface state appears to be broken up into one-dimensional quantum-well levels, indicating total electron confinement within the terraces. The angular resolution allows the probability density of the terrace quantum well state to be mapped in reciprocal space, complementing nicely the wave function measured in real space by STM. DOI: 10.1103/PhysRevLett.87.107601 PACS numbers: 79.60.Bm, 68.35.Bs, 73.21. -b Vicinal surfaces are natural templates for growing nanostructured solids with low-dimensional properties [1,2]. They also serve as model systems for studying the electron wave functions and other basic properties of lateral nanostructures [3]. Vicinal noble metal (111) surfaces are particularly suitable because they have a freeelectron-like surface state that scatters strongly at step edges, leading to one-dimensional confinement within terraces, standing-wave patterns, and step superlattice effects [4 -6]. One big advantage is that the surface state can be readily probed by both scanning tunneling microscopy/ spectroscopy (STM/STS) or photoemission [3][4][5][6][7]. Since photoemission is an averaging technique it requires regular arrays of steps over comparatively large areas to obtain meaningful results. However, most surfaces have a variety of defects and in general a broad distribution of terrace sizes. This hampers the observation of small effects such as the opening of a step superlattice gap at the edge of the Brillouin zone. In contrast, in STM a single terrace is enough to study electronic properties, such as confinement or scattering, but the reciprocal space of the superlattice cannot be properly investigated as in photoemission. It is interesting to note the difference between STM experiments that reveal total electron confinement [4,5], and photoemission results that show electron dispersion across the steps and superlattice effects [3,6,7]. Although the differences appear to be related to the average terrace size involved (large in STM, small in photoemission, [3]), in fact terrace confinement of surface states observed with photoemission has never been reported previously. Here we present clear evidence of the first two energy levels of a terrace quantum well from photoemission in agreement with STM observations. Both levels display strong angular-dependent intensity, as expected from the photoemission matrix element of one-dimensional quantum-well levels. We show how angular scans of the photoemission intensity probe in reciprocal space the same localized electron wave functions probed by STM in real space.Photoemission experiments have been performed at the SU8 undulator, Spanish-French beam line at LURE (Paris). The experiments were performed at 300 K using p-polarized light and photon ...

The oldest known magnetic material, magnetite, is of current interest for use in spintronics as a thin film. An open question is how thin can magnetite films be and still retain the robust ferrimagnetism required for many applications. We have grown 1-nm-thick magnetite crystals and characterized them in situ by electron and photoelectron microscopies including selected-area x-ray circular dichroism. Well-defined magnetic patterns are observed in individual nanocrystals up to at least 520 K, establishing the retention of ferrimagnetism in magnetite two unit cells thick.