Publications de Helmuth Berger

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We report measurements of Shubnikov-de Haas oscillations in the giant Rashba semiconductor BiTeCl under applied pressures up to similar to 2.5 GPa. We observe two distinct oscillation frequencies, corresponding to the Rashba-split inner and outer Fermi sur ...

We report a long-wavelength helimagnetic superstructure in bulk samples of the ferrimagnetic insulator Cu2OSeO3. The magnetic phase diagram associated with the helimagnetic modulation inferred from small-angle neutron scattering and magnetization measureme ...

We report ac susceptibility data on RuSr2(Eu,Ce)(2)Cu2O10-y (Ru-1222, Ce content x=0.5 and 1.0), RuSr2GdCu2O8 (Ru-1212), and SrRuO3. Both Ru-1222 (x=0.5, 1.0) sample types exhibit unexpected magnetic dynamics in low magnetic fields: logarithmic time relaxation, switching behavior, and "inverted" hysteresis loops. Neither Ru-1212 nor SrRuO3 exhibit such magnetic dynamics. The results are interpreted as evidence of the complex magnetic order in Ru-1222. We propose a specific multilayer model to explain the da

Resonant inelastic x-ray scattering in the soft x-ray regime has been profiting much from technical advances that have lowered considerably the instrumental linewidth. At the ADRESS beam line of the Swiss Light Source the SAXES spectrometer can be used to ...

Photoemission spectromicroscopy data on Si-GaSe with 0.2 mu m lateral resolution revealed laterally inhomogeneous interface Se-Si chemical reactions. The local Si 2p fits agrees with interface Si selenide parameters; the Se 3d peaks indicate a Si-selenide component; the Ga 3d peaks exhibit a metallic component whose intensity increases with Si coverage. This local interface reaction is related to lateral changes in the band lineup. (C) 1998 American Institute of Physics. [S0003-6951(98)02839-3].

We report magnetic properties of a 3d(9) (Cu2+) magnetic insulator Cu2OSO4 measured on both powder and single crystal. The magnetic atoms of this compound form layers whose geometry can be described either as a system of chains coupled through dimers or as ...

We report electron spin resonance (ESR), Raman scattering, and interband absorption measurements of the multiferroic FeTe2O5Br with two successive magnetic transitions at T-N1 = 11.0 K and T-N2 = 10.5 K. ESR measurements show all characteristics of a low-d ...

We report the observation of Shubnikov-de Haas oscillations in single crystals of the Rashba spin-splitting compound BiTeI, from both longitudinal [R-xx(B)] and Hall [R-xy(B)] magnetoresistance. Under magnetic fields up to 65 T, we resolved unambiguously o ...

Lattice dynamics of low-dimensional BaVS3 is reported across the metal-insulator Peierls transition occurring at T-P = 69 K using a combination of the thermal diffuse scattering of x rays, inelastic x-ray scattering, and density-functional theory calculati ...

V L-3 edge resonant inelastic x-ray scattering measurements performed on high quality BaVS3 single crystals reveal that the intra-t(2g) dd excitations close to the elastic peak are suppressed below the metal-insulator transition induced by the Peierls inst ...

Time- and angle-resolved photoemission spectroscopy is a powerful technique to study ultrafast electronic dynamics in solids. Here, an innovative optical setup based on a 100-kHz Yb laser source is presented. Exploiting non-collinear optical parametric amp ...

Single crystal growth by chemical vapour transport has resulted samples with Fe1.35Ge stoichiometry. Structural study has shown that the large number of vacancies introduces an incommensuately modulated structure. The electrical resistivity is in the 200 m ...

We report a comprehensive study of the paradigmatic quasi-1D compound (TaSe4)(2)I performed by means of angle-resolved photoemission spectroscopy (ARPES) and first-principles electronic structure calculations. We find it to be a zero-gap semiconductor in t ...

During the last decade, III-VI layered semiconductors (GaSe, InSe, GaS, etc.) have emerged as potential candidates for various applications, such as FET and optoelectronic devices. The properties of this class of layered materials are strongly dependent on ...

We realized ambipolar field-effect transistors by coupling exfoliated thin flakes of tungsten disulfide (WS2) with an ionic liquid dielectric. The devices show ideal electrical characteristics, including very steep subthreshold slopes for both electrons an ...

Single crystals of GaInTe2 were grown from a melt and characterized by various experimental techniques, such as x-ray diffraction, x-ray photoelectron spectroscopy (XPS), and electrical and photoluminescence (PL) measurements. Our investigation evaluated important parameters of this challenging material. In particular, we studied here for the first time the electronic structure, the excitonic effects and the impurity bound states of GaInTe2, by means of XPS and by analysing dependences on the temperature an

High-resolution angle-resolved photoemission data from the insulating phase of the charge-density-wave (CDW) material 1T-TaS2 reveal the backfolding of the electronic bands associated with the CDW superlattice, but also an additional, unexpected periodicit ...

The search for new materials for energy -efficient electronic devices has gained unprecedented importance. Among the various classes of magnetic materials driving this search are antiferromagnets, magnetoelectrics, and systems with topological spin excitat ...

We report on AC susceptibility, resistivity, thermopower and measurements of sintered magnetic superconductor RuSr2GdCu2O8. The anti ferromagnetic phase transition at 133 K is seen clearly in the AC susceptibility as well as in the derivative of resistivity and thermopower. Above the antiferromagnetic transition, we have found some new evidences of the similarity between HTC compounds and the magnetic superconductor. The onset of superconductivity is observed by both transport methods at 46 K, and an explan

We have realized ambipolar ionic liquid gated field-effect transistors based on WS2 mono- and bilayers, and investigated their opto-electronic response. A thorough characterization of the transport properties demonstrates the high quality of these devices ...

Helmuth Berger

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Evolution of the Fermi surface of BiTeCl with pressure

Long-Wavelength Helimagnetic Order and Skyrmion Lattice Phase in Cu2OSeO3

Ruthenocuprates RuSr2(Eu,Ce)(2)Cu2O10-y: Intrinsic magnetic multilayers

Crystal field and low energy excitations measured by high resolution RIXS at the L-3 edge of Cu, Ni and Mn

Band discontinuity fluctuations and local chemistry at the GaSe-Si interface

Ferrimagnetic 120 degrees magnetic structure in Cu2OSO4

Magnetic, structural, and electronic properties of the multiferroic compound FeTe2O5Br with geometrical frustration

Quantum oscillations and optical conductivity in Rashba spin-splitting BiTeI

Order-disorder type of Peierls instability in BaVS3

Opening of a Peierls gap in BaVS3 probed by V L-3 edge resonant inelastic x-ray scattering

An innovative Yb-based ultrafast deep ultraviolet source for time-resolved photoemission experiments

The influence of the incommensurately modulated structure on the physical properties of Fe1.35Ge

Electronic Instability in a Zero-Gap Semiconductor: The Charge-DensityWave in (TaSe4)(2)I

Structural investigation of InSe layered semiconductors

Quantitative Determination of the Band Gap of WS2 with Ambipolar Ionic Liquid-Gated Transistors

The growth and properties of single crystals of GaInTe2, a ternary chalcogenide semiconductor

Unexpected periodicity in the quasi-two-dimensional Mott insulator 1T-TaS2 revealed by angle-resolved photoemission

Spin-Reorientation-Driven Linear Magnetoelectric Effect in Topological Antiferromagnet Cu3TeO6

Consistent behaviour of AC susceptibility and transport properties in magnetic superconductor RuSr2GdCu2O8

Mono- and Bilayer WS2 Light-Emitting Transistors