13 research outputs found
Schichten gegen Reibung und Verschleiss bei einem Hochtemperatur Helium-Helium/Zwischenwaermetauscher
SIGLEAvailable as manuscript MS 1311/85 from VCH Verlagsgesellschaft m.b.H., Weinheim (Germany, F.R.) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
Dissimilarities between the electronic structure of chemically doped and chemically pressurized iron pnictides from an angle-resolved photoemission spectroscopy study
We have studied the electronic structure of EuFe2As2-xPx using high-resolution angle-resolved photoemission spectroscopy. Upon substituting As with the isovalent P, which leads to chemical pressure and to superconductivity, we observe a nonrigid-band-like change of the electronic structure along the center of the Brillouin zone (BZ) in the form of an orbital and kz-dependent increase or decrease in the size of the hole pockets near the Γ−Z line. The diameter of the Fermi surface cylinders at the BZ corner which form electron pockets, increases at K and changes in a nonmonotonous way at X. This is in stark contrast to p- and n-type doped iron pnictides where, on the basis of ARPES experiments, a more rigid-band-like behavior has been proposed. These findings indicate that there are different ways in which the nesting conditions can be reduced causing the destabilization of the antiferromagnetic order and the appearance of the superconducting dome
Orbital character variation of the Fermi surface and doping dependent changes of the dimensionality in BaFe2 xCoxAs2 from angle resolved photoemission spectroscopy
From a combination of high resolution angle-resolved photoemission
spectroscopy and density functional calculations, we show that BaFe2As2
possesses essentially two-dimensional electronic states, with a strong change
of orbital character of two of the Gamma-centered Fermi surfaces as a function
of kz. Upon Co doping, the electronic states in the vicinity of the Fermi level
take on increasingly three-dimensional character. Both the orbital variation
with kz and the more three-dimensional nature of the doped compounds have
important consequences for the nesting conditions and thus possibly also for
the appearance of antiferromagnetic and superconducting phases.Comment: 5 pages, 4 figure
The role of space charge in spin resolved photoemission experiments
Spin-resolved photoemission is one of the most direct ways of measuring the magnetization of a ferromagnet. If all valence band electrons contribute, the measured average spin polarization is proportional to the magnetization. This is even the case if electronic excitations are present, and thus is of particular interest for studying the response of the magnetization to a pump laser pulse. Here, we demonstrate the feasibility of ultrafast spin-resolved photoemission using free electron laser (FEL) radiation and investigate the effect of space charge on the detected spin polarization. The sample is exposed to the radiation of the FEL FLASH in Hamburg. Surprisingly, the measured spin polarization depends on the fluence of the FEL radiation: a higher FEL fluence reduces the measured spin polarization. Space-charge simulations can explain this effect. These findings have consequences for future spin-polarized photoemission experiments using pulsed photon sources