Helmuth Berger

Cette personne n’est plus à l’EPFL

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Publications associées (311)

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

Helmuth Berger

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 ...

American Physical Society2007

Fermi surface of layered compounds and bulk charge density wave systems

Helmuth Berger, Philipp Aebi, Corsin Battaglia

A review is given of recent angle-resolved photoemission (ARPES) experiments and analyses on a series of layered charge density wave materials. Important aspects of ARPES are recalled in view of its capability for bulk band, Fermi surface and spectral func ...

2007

Spin resonance in the ordered magnetic state of Ni-5(TeO3)(4)Cl-2

Helmuth Berger, László Forró, Bálint Náfrádi

The transition metal tellurium oxychloride, Ni-5(TeO3)(4)Cl-2, has been investigated by high-field electron-spin resonance for frequencies up to 3 THz, at temperatures well below the magnetic ordering at 23 K. At zero external field several resonance modes ...

2006

Incommensurate magnetic ordering in Cu2Te2O5X2 (X=Cl,Br) studied by single crystal neutron diffraction

Helmuth Berger, Henrik Moodysson Rønnow, Joël Mesot

Polarized and unpolarized neutron-diffraction studies have been carried out on single crystals of the coupled spin tetrahedra systems Cu2Te2O5X2 (X=Cl, Br). A model of the magnetic structure associated with the propagation vectors k(') (Cl) approximate to ...

2006

Electronic structure of one-dimensional copper oxide chains in LiCu2O2 from angle-resolved photoemission and optical spectroscopy

Helmuth Berger, Marco Grioni, Daniela Pacilè

Angle-resolved photoemission (ARPES) and optical measurements were performed on single crystal samples of LiCu2O2, an antiferromagnetic S=1/2 spin-chain compound. The ARPES spectra show several dispersive branches associated with hybrid copper-oxygen state ...

2006

Separation of Orbital Contributions to the Optical Conductivity of BaVS3

Helmuth Berger, László Forró, Richard Gaal, Neven Barisic, Ana Akrap

2006

Photoemission as a probe of coexisting and conflicting periodicities in low-dimensional solids

Helmuth Berger, Marco Grioni, Luca Perfetti, Christian Reinhard Ast, Daniela Pacilè

When two different periodic potentials are present at the same time in a solid, the electron wavefunctions must conform to the resulting overall periodicity. It is the case of the broken-symmetry phases which are often observed in low-dimensional systems. ...

Institute of Physics (IoP) and Deutsche Physikalische Gesellschaft2005

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

Helmuth Berger, László Forró, Giorgio Margaritondo

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 ...

2005

Incommensurate magnetism in the coupled spin tetrahedra system Cu2Te2O5Cl2

Helmuth Berger, Henrik Moodysson Rønnow, Joël Mesot

Neutron scattering studies on powder and single crystals have provided new evidence for unconventional magnetism in Cu2Te2O5Cl2. The compound is built from tetrahedral clusters of S=1/2 Cu2+ spins located on a tetragonal lattice. Magnetic ordering, emergin ...

2005

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

Thomas Gloor, Helmuth Berger, Marco Grioni, Luca Perfetti, Frédéric Mila

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 ...

2005

Mott phase at the surface of 1T-TaSe2 observed by scanning tunneling microscopy

Helmuth Berger, Marco Grioni, Luca Perfetti

In this Letter we report the observation, by scanning tunneling microscopy, of a Mott metal to insulator transition at the surface of 1T-TaSe2. Our spectroscopic data compare considerably well with previous angle-resolved photoemission spectroscopy measure ...

American Physical Society2005

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