16 research outputs found
Surface properties of SmB6 from x-ray photoelectron spectroscopy
We have investigated the properties of cleaved SmB single crystals by
x-ray photoelectron spectroscopy. At low temperatures and freshly cleaved
samples a surface core level shift is observed which vanishes when the
temperature is increased. A Sm valence between 2.5 - 2.6 is derived from the
relative intensities of the Sm and Sm multiplets. The B/Sm
intensity ratio obtained from the core levels is always larger than the
stoichiometric value. Possible reasons for this deviation are discussed. The B
signal shows an unexpected complexity: an anomalous low energy component
appears with increasing temperature and is assigned to the formation of a
suboxide at the surface. While several interesting intrinsic and extrinsic
properties of the SmB surface are elucidated in this manuscript no clear
indication of a trivial mechanism for the prominent surface conductivity is
found
Band dependent emergence of heavy quasiparticles in CeCoIn5
We investigate the low temperature (T 2 K) electronic structure of the
heavy fermion superconductor CeCoIn5 (T = 2.3 K) by angle-resolved
photoemission spectroscopy (ARPES). The hybridization between conduction
electrons and f-electrons, which ultimately leads to the emergence of heavy
quasiparticles responsible for the various unusual properties of such
materials, is directly monitored and shown to be strongly band dependent. In
particular the most two-dimensional band is found to be the least hybridized
one. A simplified multiband version of the Periodic Anderson Model (PAM) is
used to describe the data, resulting in semi-quantitative agreement with
previous bulk sensitive results from de-Haas-van-Alphen measurements.Comment: 6 pages, 3 figure
Observation of strontium segregation in LaAlO3 SrTiO3 and NdGaO3 SrTiO3 oxide heterostructures by X ray photoemission spectroscopy
LaAlO3 and NdGaO3 thin films of different thicknesses have been grown by pulsed laser deposition on TiO2-terminated SrTiO3 single crystals and investigated by soft X-ray photoemission spectroscopy. The surface sensitivity of the measurements has been tuned by varying photon energy hν and emission angle Θ. In contrast to the core levels of the other elements, the Sr 3d line shows an unexpected splitting for higher surface sensitivity, signaling the presence of a second strontium component. From our quantitative analysis we conclude that during the growth process Sr atoms diffuse away from the substrate and segregate at the surface of the heterostructure, possibly forming strontium oxide
X-ray photoemission study of Ce T In 5 ( T = Co, Rh, Ir)
We investigated CeTIn5 (T = Co, Rh, Ir) using temperature- and angle-dependent x-ray photoemission spectroscopy. The Ce 3d core level has a very similar shape for all three materials and is indicative of weak f-hybridization. The spectra were analyzed using a simplified version of the Anderson impurity model, which yields a Ce 4f occupancy that is larger than 0.9. The temperature dependence shows a continuous, irreversible and exclusive broadening of the Ce 3d peaks, due to oxidation of Ce at the surface
Site-selective spectroscopy with depth resolution using resonant x-ray reflectometry
Abstract Combining dissimilar transition metal oxides (TMOs) into artificial heterostructures enables to create electronic interface systems with new electronic properties that do not exist in bulk. A detailed understanding of how such interfaces can be used to tailor physical properties requires characterization techniques capable to yield interface sensitive spectroscopic information with monolayer resolution. In this regard resonant x-ray reflectivity (RXR) provides a unique experimental tool to achieve exactly this. It yields the element specific electronic depth profiles in a non-destructive manner. Here, using a YBa2Cu3O7−δ (YBCO) thin film, we demonstrate that RXR is further capable to deliver site selectivity. By applying a new analysis scheme to RXR, which takes the atomic structure of the material into account, together with information of the local charge anisotropy of the resonant ions, we obtained spectroscopic information from the different Cu sites (e.g., chain and plane) throughout the film profile. While most of the film behaves bulk-like, we observe that the Cu-chains at the surface show characteristics of electron doping, whereas the Cu-planes closest to the surface exhibit an orbital reconstruction similar to that observed at La1−x Ca x MnO3/YBCO interfaces