Publications de Helmuth Berger

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Angle-resolved photoemission spectra taken with high energy resolution on the one-dimensional compound (TaSe4)2I confirm the suppression of the spectral intensity at the Fermi edge for one-dimensional systems and lend support to correlation effects as its most probable cause.

We present the resistivity measurements on single crystals of Sr2RuO4-delta, grown by the flux technique. We discuss the striking, linear temperature dependence of resistivity that persists up to similar to 1050 K. The superconductivity in this system is confined below 1 K. This result suggests that the non-Fermi-liquid-alike linear temperature dependence of resistivity is not an exclusive signature of the anomalous normal stare of high-T-c cuprates but rather of layered oxides in general, especially perovs

The high-T-c cuprate superconductors are close to antiferromagnetic order. Recent measurements of magnetic excitations have reported an intriguing similarity to the spin wavesmagnons- of the antiferromagnetic insulating parent compounds, suggesting that ma ...

Cobalt-doping of Bi2Sr2CaCu2Ox beyond a critical level of 1.5-1.7 at % produces both a large decrease in the superconducting transition critical temperature and all of the classic symptoms of Anderson localization. These include: a negative slope of the ab-plane resistivity vs temperature, no dispersing states near the Fermi level and a decrease of the photoemission signal in the same region.

High-resolution angle-resolved photoemission data show that a metal-insulator Mott transition occurs at the surface of the quasi-two-dimensional compound 1T-TaSe2. The transition is driven by the narrowing of the Ta 5d band induced by a temperature-dependent modulation of the atomic positions. A dynamical mean-field theory calculation of the spectral function of the half-filled Hubbard model captures the main qualitative feature of the data, namely, the rapid transfer of spectral weight from the observed qu

We present a detailed study of the phase diagram of copper-intercalated TiSe2 single crystals, combining local Hall-probe magnetometry, tunnel diode oscillator technique (TDO), and specific-heat and angle-resolved photoemission spectroscopy measurements. A ...

Using angle-resolved photoemission and linearly polarized synchrotron radiation, we measured the electronic band structure of electronic states of CuO2 plane materials ranging from insulators (Sr2CuO2Cl2) to overdoped superconductors (Bi2Sr2CaCu2O8+x). We report three results: (i) The CuO2 containing insulator possesses a spin-density-wave (SDW) ground state; (ii) there are precursors df the SDW state for underdoped Bi2Sr2CaCu2O8+x; (iii) an extended saddle-point-type van Hove singularity is neither a neces

We report temperature-dependent angle-resolved photoemission spectra for overdoped Bi2Sr2CaCu2O8+alpha single-crystal samples. The data indicate that there is a special temperature (T+) where the spectral function changes intensity, and where the energy difference between the peak and dip features changes. The data also demonstrate that immediately above the superconducting transition temperature, the system exhibits a non-lorentzian lineshape. We discuss implications of the data.

We exploit time- and angle-resolved photoemission spectroscopy to determine the evolution of the out-of-equilibrium electronic structure of the topological insulator Bi2Se3. The response of the Fermi-Dirac distribution to ultrashort IR laser pulses has bee ...

The first photoelectron spectromicroscopy experiments at the new 1.3 GeV ultrabright X-ray source of SRRC have produced interesting results concerning chemical and topographic features in three types of systems: neuron networks grown on metal substrates, cleaved surfaces of high-quality single crystals of Bi2Ca2SrCu2Ox (BCSCO) and Au-covered GaSe. In the case of BCSCO, a general tendency to chemical homogeneity - extremely important for sophisticated spectroscopic applications - sharply conflict with occasi

The material ZrTe3 is a well-known example of an incommensurate periodic lattice distortion (PLD) at low temperatures due to a charge density wave (CDW). Previous studies have found a sharp boundary as a function of pressure between CDW below 5 GPa and bul ...

We investigate the polaronic ground state of anatase TiO2 by bulk-sensitive resonant inelastic x-ray spectroscopy (RIXS) at the Ti L-3 edge. We find that the formation of the polaron cloud involves a single 95 meV phonon along the c axis, in addition to th ...

The interpretation of photoemission-spectromicroscopy studies of Au on GaSe requires a revision of established ideas about this interface, which has long been considered a prototype of Schottky-like systems. We find that the interface-formation process involves strong substrate-overlayer interactions, the release of free Ga, and the formation of interface species, and leads to a barrier height in total disagreement with the Schottky model. Furthermore, the space-resolving capabilities of our instruments rev

The comment by Starnberg, Brauer, and Nilsson qualitatively identifies the final-state lifetime as the cause of the ''anomalous'' photoemission broadening, but it neglects the linear energy dependence of the final-state broadening whose effect is of the same magnitude as the purely geometrical contributions.

We reject the assertion of Claessen et al., confirm the validity of our data, and discuss possible causes for the disagreement.

The longitudinal low frequency acoustic and optic phonon modes of 2H-NbSe2 have been determined for the Gamma - M direction with inelastic neutron scattering at 50 K close to the charge density wave transition temperature. ...

In the giant Rashba semiconductor BiTeI, electronic surface scattering with Lorentzian linewidth is observed that shows a strong dependence on surface-termination and surface-potential shifts. A comparison with the topological insulator Bi2Se3 evidences th ...

The recent discovery of magnetic skyrmion lattices initiated a surge of interest in the scientific community. Several novel phenomena have been shown to emerge from the interaction of conducting electrons with the skyrmion lattice, such as a topological Ha ...

The dynamics of the photoinduced commensurate-to-incommensurate charge density wave (CDW) phase transition in 4H(b)-TaSe2 are investigated by femtosecond electron diffraction. In the perturbative regime, the CDW re-forms on a 150-ps time scale, which is tw ...

The lattice dynamics of low-dimensional BaVS3 is reported across the hexagonal-orthorhombic phase transition occurring at T-S = 250 K using a combination of the thermal diffuse scattering of x rays, inelastic x-ray scattering, and density functional theory ...

Helmuth Berger

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Photoemission near the Fermi Energy in One Dimension

Linear resistivity from similar to 1 to 1050 K in Sr2RuO4-delta single crystals grown by the flux technique

Anisotropic softening of magnetic excitations along the nodal direction in superconducting cuprates

Co-doped Bi2Sr2CaCu2Ox: Anderson localization and superconductivity

Spectroscopic signatures of a bandwidth-controlled Mott transition at the surface of 1T-TaSe2

Magnetic and thermodynamic properties of CuxTiSe2 single crystals

Electronic structure of CuO2 planes: From insulator to superconductor

Temperature-dependent photoemission features for overdoped Bi2Sr2CaCu2O8+x cuprates

Ultrafast photodoping and effective Fermi-Dirac distribution of the Dirac particles in Bi2Se3

First Spectromicroscopy Tests at the Taiwan Synchrotron-Radiation Research-Center (SRRC) - Chemical and Topographic Microimaging of Layered Systems

Evolution of the charge density wave superstructure in ZrTe3 under pressure

Electron-Phonon Coupling in the Bulk of Anatase TiO2 Measured by Resonant Inelastic X-Ray Spectroscopy

Microscopic-Scale Lateral Inhomogeneities of the Schottky-Barrier-Formation Process

Lifetime Broadening in Bulk Photoemission Spectroscopy - Reply

Temperature dependence of electronic states in (TaSe4)(2)I - Reply

Temperature dependent phonon dispersion in 2H-NbSe2 investigated using inelastic neutron scattering

Enhanced quasiparticle dynamics of quantum well states: The giant Rashba system BiTeI and topological insulators

Dramatic pressure-driven enhancement of bulk skyrmion stability

Ultrafast Dynamics of Charge Density Waves in 4H(b)-TaSe2 Probed by Femtosecond Electron Diffraction

Soft-phonon driven hexagonal-orthorhombic phase transition in BaVS3