Publications by Helmuth Berger

Chat with Graph Search

Ask any question about EPFL courses, lectures, exercises, research, news, etc. or try the example questions below.

DISCLAIMER: The Graph Chatbot is not programmed to provide explicit or categorical answers to your questions. Rather, it transforms your questions into API requests that are distributed across the various IT services officially administered by EPFL. Its purpose is solely to collect and recommend relevant references to content that you can explore to help you answer your questions.

Using high-resolution angle-resolved photoemission spectroscopy we have studied the momentum and photon energy dependence of the anomalous high-energy dispersion, termed waterfalls, between the Fermi level and 1 eV binding energy in several high-T-c superc ...

We report on the spin dynamics and discovery of magnetoelectricity in the coupled-spin tetrahedral compound Cu2Te2O5Cl2. Te-125 NMR measurements show an anomalous resonance frequency shift and a signal wipe-out phenomenon around the Neel temperature T-N = ...

A skyrmion state in a noncentrosymmetric helimagnet displays topologically protected spin textures with profound technological implications for high-density information storage, ultrafast spintronics, and effective microwave devices. Usually, its equilibri ...

The Dzyaloshinskii-Moriya interaction (DMI) has an impact on excited spin waves in the chiral magnet Cu2OSeO3 by means of introducing asymmetry in their dispersion relations. The confined eigenmodes of a chiral magnet are hence no longer the conventional s ...

Magnetic skyrmions in chiral magnets are nanoscale, topologically protected magnetization swirls that are promising candidates for spintronics memory carriers. Therefore, observing and manipulating the skyrmion state on the surface level of the materials a ...

Photoelectron-spectromicroscopy experiments unexpectedly revealed a reacted phase for Ge overlayers on GaSe. This finding is in sharp contrast with the notion that this interface is an ideal Schottky system, whose band discontinuities, for example, are determined by the Anderson rule-and with the widespread belief that most III-VI-based interfaces behave like Schottky systems. After this result, to the best of our knowledge, no heterojunction is known that matches the requisites of an ideal Schottky system.

We studied the newly synthesized quasi-one-dimensional compound Nb4Te17I4. Resistivity measurements confirmed its pseudo-one-dimensional character and photoemission spectroscopy clarified the nature of its valence band states. This polytelluride is a narrow-gap semiconductor at room temperature, with a forbidden gap width of 0.34 eV.

We present a detailed low-temperature scanning tunneling microscopy (STM) study of the commensurate charge density wave (CDW) in 1T-TiSe2 in the presence of single atom defects. We find no significant modification of the CDW lattice in single crystals with ...

We perform scanning photocurrent microscopy on WS2 ionic liquid-gated field effect transistors exhibiting high-quality ambipolar transport. By properly biasing the gate electrode, we can invert the sign of the photocurrent showing that the minority photoca ...

Scanning photoelectron spectromicroscopy experiments on the edge of patterned Si overlayers on GaSe revealed the presence of an inhomogeneous reaction with a metallic-like Ga phase separation. The Si-Se chemically shifted components show lateral variations and a thickness-related SiSe2/SiSex (x = 0.5, 1, and 1.5) ratio on a micrometer scale. The dependence of the peak intensities on the overlayer thickness suggests an initial layer-by-layer coverage until approximate to 2 Angstrom, followed by a clustering

High-energy-resolution photoemission spectra, taken on three quasi-one-dimensional crystals, TaTe4, NbTe4, and (NbSe4)3I confirm the general phenomenon of the suppression of the photoemission intensity near the Fermi level in one dimension. We analyze the possible causes of this phenomenon in light of previous results on (TaSe4)2I.

We report here on the results obtained by the CERN RD26 collaboration on the production and characterization of large area photocathodes, susceptible to equip fast UV-photon imaging devices. Such detectors are planned for some Ring Imaging Cherenkov (RICH) detector projects, in particular HADES at SIS Darmstadt, BABAR at the SLAG asymmetric B-factory, and ALICE at the LHC (CERN).

We performed a spectromicroscopy experiment to find evidence of lateral inhomogeneities in the band bending for the Al/GaS system. Microimages of the interface tuned on the Al 2p con levels revealed localized chemical inhomogeneities in proximity of the edge of the Al overlayer. A careful analysis of the photoemission spectra supports these conclusions and relates the inhomogeneities to band bending variations. The micron-size lateral scale for these features is similar to that of other interfaces. (C) 1999

Angle-resolved, synchrotron-radiation photoemission and low-energy electron-diffraction studies of single-crystal Bi2Sr2CaCu2Ox high-temperature superconductors establish that the [100] and [010] directions exhibit quantitatively different structural and electronic properties. Specifically, there is a superlattice modulation in the [010] direction, with superlattice period between 4.7 and 5.2 times the period in the [100] direction. Accompanying this structural difference there is a marked difference in the

Local inversion symmetry breaking in centrosymmetric materials can lead to large spin polarization of the electronic band structure in separate sectors of the unit cell. Here, the authors reveal such hidden spin polarisation in ZrSiTe using spin and angle ...

We report the results of a low-temperature (300 K-15 K) high-pressure (up to 22 GPa) Raman study of the Verwey transition in magnetite (Fe3O4). We use additional Raman modes observed below the Verwey transition to determine how the transition temperature c ...

Photoemission spectromicroscopy experiments on a series of Y-doped Bi2Sr2Ca1Cu2O8 single crystals show that the doping changes the valence of copper as required for the observed modification of the critical temperature. The doping, however, affects with substitutional reactions not only the CaO planes, but also the SrO planes.

Ferromagnetism was found to coexist with superconductivity in Dy-doped BiPbSrCaCuO-2212 single crystals up to the superconducting critical temperature T-c similar to 80 X. Several experimental tests indicated that the phenomenon is intrinsic to the entire specimen rather than due to separate phases or to isolated impurities.

Helmuth Berger

Chat with Graph Search

Momentum and energy dependence of the anomalous high-energy dispersion in the electronic structure of high temperature superconductors

Spin dynamics and magnetoelectric properties of the coupled-spin tetrahedral compound Cu2Te2O5Cl2

Room-temperature skyrmion phase in bulk Cu2OSeO3 under high pressures

Confined dipole and exchange spin waves in a bulk chiral magnet with Dzyaloshinskii-Moriya interaction

Multidomain Skyrmion Lattice State in Cu2OSeO3

Spectromicroscopic evidence of Ge-GaSe chemical reactions: Not a Schottky system

On the electronic properties of the quasi-one-dimensional crystal Nb4Te17I4

Scanning tunneling microscopy of the charge density wave in 1T-TiSe2 in the presence of single atom defects

Scanning photocurrent microscopy reveals electron-hole asymmetry in ionic liquid-gated WS2 transistors

Inhomogeneous and thickness-dependent chemical reactivity at GaSe-Si interfaces

High-Resolution Tests of Low-Dimensionality Effects in Photoemission

Recent Results on the Properties of CsI Photocathodes

A spectromicroscopy study of the Al GaS interface: Evidence of band bending lateral inhomogeneities

Photoemission Response of Bi2sr2cacu2ox - the Normal-State Anisotropy Is Intrinsic

Hidden bulk and surface effects in the spin polarization of the nodal-line semimetal ZrSiTe

Influence of point defects on the metal-insulator transition in BaVS3

Magnetite: Raman study of the high-pressure and low-temperature effects

The effect of Yttrium on the Ca and Sr planes of Y-doped Bi2Sr2Ca1Cu2O8

Coexistence of ferromagnetism and high-temperature superconductivity in Dy-doped BiPbSrCaCuO

THz Generation and Detection on Dirac Fermions in Topological Insulators