TY  - JOUR
A1  - Rader, Oliver
A1  - Fauth, K.
A1  - Gould, C.
A1  - Ruster, C.
A1  - Schott, G. M.
A1  - Schmidt, G.
A1  - Brunner, K.
A1  - Molenkamp, Laurens W.
A1  - Schutz, G.
A1  - Kronast, F.
A1  - Durr, H. A.
A1  - Eberhardt, W.
A1  - Gudat, Wolfgang
T1  - Identification of extrinsic Mn contributions in Ga1-xMnxAs by field-dependent magnetic circular X-ray dichroism
N2  - We combine sensitivity to atomic number, chemical shifts, probing depth, and magnetic order in a field- dependent magnetic circular X-ray dichroism study at the Mn L-edge of the diluted ferromagnetic semiconductor Ga1-xMnxAs and observe different Mn constituents: ferromagnetic Mn with an n(d) > 5 lineshape and paramagnetic Mn with distinct n(d) = 5 lineshape. The paramagnetic Mn is assigned to interstitials with surface segregation tendency. (c) 2005 Elsevier B.V. All rights reserved
Y1  - 2005
SN  - 0368-2048
ER  - 
TY  - JOUR
A1  - Varykhalov, Andrei
A1  - Rader, Oliver
A1  - Gudat, Wolfgang
T1  - Structure and quantum-size effects in a surface carbide : W(110)/C-R(15 X 3)
N2  - Results of the combined investigation of atomic and electronic structure of the W(110)/C-R(15x3) surface carbide are reported. A variety of experimental techniques has been involved such as scanning tunneling microscopy (STM), low-energy electron diffraction, x-ray photoelectron spectroscopy, and angle-resolved photoemission (ARPES). Distance-dependent STM measurements show a nontrivial geometrical behavior in the topography data, demonstrating five different patterns representing the superstructure at different values of the tip-surface separation. Atomic resolution was achieved at lower tunneling gap resistance. An unexpected spatial asymmetry in the distribution of the local density of states across the surface unit cell has been observed as well. Photoelectron spectroscopy of C1s and W4f core levels clarifies the nature of the chemical bonding in the system. The band mapping with ARPES provides information on the wave- vector dependence of the electronic states. Notable quantum size and superlattice effects were discovered in the dispersion of the valence-band states. The experimental data suggests an apparent one-dimensional character of the electronic structure. Lateral quantization and umklapp scattering are proposed as explanation. Finally, based on photoemission and STM measurements, an improved crystallographic model of the tungsten surface carbide is introduced
Y1  - 2005
SN  - 1098-0121
ER  - 
TY  - JOUR
A1  - Varykhalov, Andrei
A1  - Shikin, A. M.
A1  - Gudat, Wolfgang
A1  - Moras, P.
A1  - Grazioli, C.
A1  - Carbone, C.
A1  - Rader, Oliver
T1  - Probing the ground state electronic structure of a correlated electron system by quantum well states: Ag/ Ni(111)
N2  - The ground state electronic properties of the strongly correlated transition metal Ni are usually not accessible from the excitation spectra measured in photoelectron spectroscopy. We show that the bottom of the Ni d band along [111] can be probed through the energy dependence of the phase of quantum-well states in Ag/Ni(111). Our model description of the quantum-well energies measured by angle-resolved photoemission determines the bottom of the Lambda(1) d band of Ni as 2.6 eV, in full agreement with standard local density theory and at variance with the values of 1.7-1.8 eV from direct angle-resolved photoemission experiments of Ni
Y1  - 2005
SN  - 0031-9007
ER  -