The Materials Science beamline at the Swiss Light Source has been operational since 2001. In late 2010, the original wiggler source was replaced with a novel insertion device, which allows unprecedented access to high photon energies from an undulator installed in a medium-energy storage ring. In order to best exploit the increased brilliance of this new source, the entire front-end and optics had to be redesigned. In this work, the upgrade of the beamline is described in detail. The tone is didactic, from which it is hoped the reader can adapt the concepts and ideas to his or her needs.

Soft-X-ray angle-resolved photoelectron spectroscopy (ARPES) with photon energies around 1 keV combines the momentum space resolution with increasing probing depth. The concepts and technical realisation of the new soft-X-ray ARPES endstation at the ADRESS beamline of SLS are described. The experimental geometry of the endstation is characterized by grazing X-ray incidence on the sample to increase the photoyield and vertical orientation of the measurement plane. The vacuum chambers adopt a radial layout allowing most efficient sample transfer. High accuracy of the angular resolution is ensured by alignment strategies focused on precise matching of the X-ray beam and optical axis of the analyzer. The high photon flux of up to 10(13) photons s(-1) (0.01% bandwidth)(-1) delivered by the beamline combined with the optimized experimental geometry break through the dramatic loss of the valence band photoexcitation cross section at soft-X-ray energies. ARPES images with energy resolution up to a few tens of meV are typically acquired on the time scale of minutes. A few application examples illustrate the power of our advanced soft-X-ray ARPES instrumentation to explore the electronic structure of bulk crystals with resolution in three-dimensional momentum, access buried heterostructures and study elemental composition of the valence states using resonant excitation.

Macroscopic ferroelectric order in α-GeTe with its noncentrosymmetric lattice structure leads to a giant Rashba spin splitting in the bulk bands due to strong spin-orbit interaction. Direct measurements of the bulk band structure using soft x-ray angle-resolved photoemission (ARPES) reveals the three-dimensional electronic structure with spindle torus shape. By combining high-resolution and spin-resolved ARPES as well as photoemission calculations, the bulk electronic structure is disentangled from the two-dimensional surface electronic structure by means of surface capping, which quenches the complex surface electronic structure. This unravels the bulk Rashba-split states in the ferroelectric Rashba α-GeTe(111) semiconductor exhibiting a giant spin splitting with Rashba parameter α R around 4.2 eVÅ, the highest of so-far known materials. DOI: 10.1103/PhysRevB.94.205111 In spintronics an important goal is to be able to control the spin of the electron in solids without applying magnetic fields [1,2]. The most promising mechanism is based on the Rashba effect [3] and the subsequent spin precession induced in such systems [4]. While most research has previously focused on 2D electron systems [5,6], recently a threedimensional (3D) form of such Rashba effect was found in a series of bismuth tellurohalides BiTeX (X = I, Br, or Cl) [7][8][9][10][11][12]. Although these materials exhibit a very large spin splitting, they lack an important property concerning functionalization, namely, the possibility to switch or tune the spin texture. This limitation can be overcome in a new class of functional materials displaying Rashba splitting coupled to ferroelectricity, the so-called ferroelectric Rashba semiconductors (FERS) [13,14].Recent photoemission experiments on α-GeTe-the stable rhombohedral room temperature configuration of the GeTe phase change material [15]-indicate that this system is a hallmark candidate for entanglement of the ferroelectric and spin-orbit order [16,17]. Due to the giant Rashba splitting spin injection from magnetic systems into GeTe appears viable in order to achieve spin-to-charge conversion [18]. Therefore, ferroelectric [13] or multiferroic [19] Rashba semiconductors bring new multifunctional assets for spintronic devices. A crucial issue for the understanding of FERS is to disentangle the Rashba effect in the bulk caused by the bulk ferroelectric lattice distortion and surface effects arising from particular surface terminations and/or possible band bendings. This represents a major challenge for surface sensitive techniques such as angle-resolved photoemission (ARPES). For this reason up to now ARPES measurements on α-GeTe surfaces performed in the surface-sensitive UV regime have been dominated by surface effects [16,17] and clear information of the three-dimensional bulk electronic structure and its spin texture has not been obtained.

The character of the surface state wave function on regularly stepped Cu(111) is reinvestigated. It is shown that the qualitative change at terrace lengths around 17 A observed previously by Ortega et al. [Phys. Rev. Lett. 84, 6110 (2000)]] must necessarily be described as a change from a propagating superlattice state to a terrace-confined quasi-one-dimensional state. This reconciles previous, apparently contradictory experimental results and sheds new light on the behavior of nearly free electrons in nanostructures. Possible mechanisms driving the localization are discussed on the basis of the surface state bulk penetration depth, which has been measured in both regimes.

The Surface/Interface: Microscopy beamline of the Swiss Light Source started operation in 2001. In 2007 the beamline has been significantly upgraded with a second refocusing section and a blazed grating optimized for high photon flux. Two Apple II type undulators with a plane grating monochromator using the collimated light scheme deliver photons with an energy from 90 eV to about 2 keV with variable polarization for the photoemission electron microscope (PEEM) as the primary user station. We measured a focus of (45 × 60) µm (v × h) and a photon flux > 10 12 photon/s for all gratings. Polarization switching within a few seconds is realized with the small bandpass of the monochromator and a slight detuning of the undulator.