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Focused ion irradiation of insulating diamond-like carbon (DLC) films is a well-recognized approach to write defined nanostructures with drastically changed properties compared to the unexposed matrix. In particular, the electrical conductivity of the film areas that are irradiated increases by several orders of magnitude. Furthermore it is known that the conductivity increase is directly related to the irradiation-induced sp3–sp2 rehybridization. This experimental work shows in detail that ion-induced microstructural ordering of the carbon atom arrangement far beyond the sp3–sp2 conversion saturation is an important microscopic mechanism for the alteration of physical properties, including an increase in the conductivity. The atomic ordering correlates with the local energy density deposited during the ion impact. Thus the ion-induced phase transformation of DLC is proposed to comprise a rehybridization stage, caused by nuclear collisions, and a rearrangement stage (graphite-like ordering) that is thermally driven by the ion impact. These conclusions are based on in-depth investigations of amorphous DLC films that were locally irradiated by a number of ion species employing several temperature regimes. The ion irradiation experiments cover a wide range of fluences. X-ray photoelectron spectroscopy, μ-Raman spectroscopy, transmission electron microscopy, and low temperature transport measurements have been applied to characterize the films.

Here we apply high resolution angle-resolved photoemission spectroscopy (ARPES) using a wide excitation energy range to probe the electronic structure and the Fermi surface topology of the Ba 1− x K x Fe 2 As 2 ( T c = 32 K) superconductor. We find significant deviations in the low energy band structure from that predicted in calculations. A set of Fermi surface sheets with unexpected topology is detected at the Brillouin zone boundary. At the X -symmetry point the Fermi surface is formed by a shallow electron-like pocket surrounded by four hole-like pockets elongated in Γ − X and Γ − Y directions.

While the pronounced doping dependence of the quasiparticle spectral weight in the antinodal region of the superconducting cuprates, as seen by ARPES, unambiguously points to the magnetic origin of the strong electron-boson coupling there, the nature of the electron scattering in the nodal direction remained unclear. Here we present a short review of our recent detailed investigations of the nodal direction of Bi-2212. Our findings prove the existence of well defined quasiparticles even in the pseudogap state and show that the essential part of the quasiparticle scattering rate, which appears on top of Auger-like electron-electron interaction, also implies a magnetic origin., 6 revtex pages, short review, presented at SNS 2004

We report studies of the electronic structure and elementary excitations of doped and undoped cuprate chains, ladders and planes. Using high energy spectroscopies such as x-ray absorption, core level photoemission and angle resolved photoemission spectroscopy, important information regarding the charge distribution and hole dynamics can be obtained. The comparison of the experimental data with suitable theoretical models sets constraints on the parameters entering into the model calculations, and offers insight into the important physical quantities governing the electronic structure of these materials. Recurring themes include the importance of the dimensionality of the Cu-O network (1D->2D) and the crucial role played by the spin-background in determining the dynamics of low-lying excitations in these strongly correlated systems., J. Electron Spec. Relat. Phenom.: special issue on electron correlation, in press

We show that the photoelectron spectrum of YBCO-123 generally includes two components. The one, which is the most pronounced, is characterized by unusually high hole doping level and exhibits no superconducting gap, while the other component retains superconductivity. We believe, the occurrence of these two components in ARPES spectra was one of the reasons that caused difficulties with the interpretation of earlier ARPES data of this compound.

The Cu substitution by Zn and Ni impurities and its influence on the mass renormalization effects in angle resolved photoelectron spectra (ARPES) of Bi 2 Sr 2 CaCu 2 O 8+ δ is addressed. We show that the nonmagnetic Zn atoms have much stronger effect both in nodal and antinodal parts of the Brillouin zone than magnetic Ni. The observed changes are consistent with the behaviour of the spin resonance mode as seen by inelastic neutron scattering in YBCO-123. This strongly suggests that the “peak-dip-hump” and the “kink” in ARPES on the one side and neutron resonance on the other are closely related features.