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SESAME and a consortium of five Helmholtz Centers are designing and installing a state-of-the-art soft X-Ray undulator beamline at the SESAME light source in Amman, Jordan. Funding is provided by the Helmholtz Association over a four year project cycle that started in January 2019. This is an interim report covering the first 36 months of the project where the construction and installation has been almost completed and commissioning and characterization of the beamline is about to start. Additionally, seminars, workshops, and a training program are part of the project aimed at establishing a broad user community.

The HESEB (Helmholtz-SESAME soft X-ray beamline) project is an initiative by the Helmholtz Association of German Research Centers (HGF) to implement a new beamline at SESAME for scientific applications using soft X-ray spectroscopy techniques. The beamline design, procurement, and construction are being carried out by a consortium of the HGF centers DESY, FZJ, HZB, HZDR and KIT in collaboration with SESAME. The new beamline will be available for the SESAME user community within the four year project duration. It will allow for a large number of top-class scientific applications and provide new cooperation potentials with German and international research groups. The beamline is based on a variable-polarization undulator and a plane-grating monochromator covering an energy range 80 - 2000 eV. The optical design and the technical specifications have been completed and a call for tender procedure is ongoing. It is expected that the beamline will see first light in summer 2021. During the course of the project, the main goals to be achieved are (i) the construction and commissioning of the beamline at SESAME with a chamber for cultural heritage applications using spatially resolved soft X-ray fluorescence, (ii) the leveraging of additional contributions from the SESAME member countries to promote the build-up of international user consortia and to secure funding for experimental endstations and additional instrumentation, (iii) the training of SESAME staff at participating Helmholtz centers to enable reliable operation of the beamline by local staff, and (iv) the fostering of the establishment of a broad user community of HESEB from the SESAME member states through training, workshops, and schools. The first soft X-ray HESEB science workshop will take place in Istanbul beginning of 2020.

Physical review / B 97(3), 035110 (2018). doi:10.1103/PhysRevB.97.035110, We present a detailed study of the Ti $3d$ carriers at the interface of $LaAlO_{3}/SrTiO_3$ heterostructures by high-resolution resonant inelastic soft x-ray scattering (RIXS), with special focus on the roles of overlayer thickness and oxygen vacancies. Our measurements show the existence of interfacial Ti $3d$ electrons already below the critical thickness for conductivity. The (total) interface charge carrier density increases up to a $LaAlO_3$ overlayer thickness of 6 unit cells before it levels out. Furthermore, we observe strong Ti $3d$ charge carrier doping by oxygen vacancies. The RIXS data combined with photoelectron spectroscopy and transport measurements indicate the simultaneous presence of localized and itinerant charge carriers. At variance with previous interpretations, we show that in our excitation energy dependent RIXS measurements the amounts of localized and itinerant Ti $3d$ electrons in the ground state do not scale with the intensities of the Raman and fluorescence peaks, respectively. Rather, we attribute the observation of either Raman components or fluorescence signal to the specific nature of the intermediate state reached in the RIXS excitation process., Published by APS, Woodbury, NY

The interfaces between two condensed phases often exhibit emergent physical properties that can lead to new physics and novel device applications and are the subject of intense study in many disciplines. We here apply experimental and theoretical techniques to the characterization of one such interesting interface system: the two-dimensional electron gas (2DEG) formed in multilayers consisting of SrTiO3 (STO) and GdTiO3 (GTO). This system has been the subject of multiple studies recently and shown to exhibit very high carrier charge densities and ferromagnetic effects, among other intriguing properties. We have studied a 2DEG-forming multilayer of the form [6 unit cells (u.c.) STO/3 u.c. of GTO](20) using a unique array of photoemission techniques including soft and hard x-ray excitation, soft x-ray angle-resolved photoemission, core-level spectroscopy, resonant excitation, and standing-wave effects, as well as theoretical calculations of the electronic structure at several levels and of the actual photoemission process. Standing-wave measurements below and above a strong resonance have been exploited as a powerful method for studying the 2DEG depth distribution. We have thus characterized the spatial and momentum properties of this 2DEG in detail, determining via depth-distribution measurements that it is spread throughout the 6 u.c. layer of STO and measuring the momentum dispersion of its states. The experimental results are supported in several ways by theory, leading to a much more complete picture of the nature of this 2DEG and suggesting that oxygen vacancies are not the origin of it. Similar multitechnique photoemission studies of such states at buried interfaces, combined with comparable theory, will be a very fruitful future approach for exploring and modifying the fascinating world of buried-interface physics and chemistry.

The electronic structure of Heusler alloys having mixed magnetic phases, comprising of vicinal anti-ferromagnetic and ferromagnetic orders, is of great significance. We present the results of an electronic structure study on Ni_(x)Cu_(1−x)MnSb Heusler alloys, using Mn-2p core-level photoemission spectroscopy. Room temperature data in the paramagnetic phase reveal a non-monotonic variation of both electron correlation strength and conduction-band hybridization such that the former enhances while the latter weakens for compositions showing a mixed phase relative to compositions at the phase boundaries to the ordered phases. The results suggest a possible electronic driving force for settling mixed-magnetic phases.