Université de Neuchâtel

Charge density waves in 1T-TaS2: an angle-resolved photoemission study

Clerc, Florian ; Bovet, M. ; Berger, Helmuth ; Despont, Laurent ; Koitzsch, Christian ; Garnier, Michael Bernard Gunnar ; Aebi, Philipp

In: Surface Science, 2006, vol. 351, no. 3-4, p. 245-249

The transition metal dichalcogenide 1T-TaS2 is a layered material exhibiting charge density waves. Based on angle-resolved photoemission experiments mapping spectral weight at the Fermi surface and density functional theory calculations we discuss possible mechanisms involved with the creation of charge density waves. At first the flat parts of the elliptically shaped Fermi...

Université de Neuchâtel

X-ray photoelectron diffraction study of Cu(1 1 1): Multiple scattering investigation

Despont, Laurent ; Naumovic, D. ; Clerc, Florian ; Koitzsch, Christian ; Garnier, Michael Bernard Gunnar ; Garcia de Abajo, F.J. ; Van Hove, M. A. ; Aebi, Philipp

In: Surface Science, 2006, vol. 600, no. 2, p. 380-385

Multiple scattering theory based on a cluster model is used to simulate full-hemispherical X-ray photoelectron diffraction measurements in order to verify how state of the art multiple scattering simulations are able to reproduce the experiment. This approach is applied to the Cu(1 1 1) surface for two different photoelectron kinetic energies. Differences and similarities between single and...

Université de Neuchâtel

Fermi-surface topology of rare-earth dihydrides

Koitzsch, Christian ; Hayoz, J. ; Bovet, M ; Clerc, Florian ; Despont, Laurent ; Ambrosch-Draxl, Claudia ; Aebi, Philipp

In: Physical Review B, 2004, vol. 70, no. 165114, p. 1-10

We report high-resolution angle-resolved photoemission experiments on epitaxial thin films of different rare-earth (RE) dihydrides (RE=Gd,La) and of YH2 and ScH2 . It is found through ab initio calculations and confirmed by Fermi surface mapping that the electronic structure becomes very similar upon hydrogenation, rendering the studied dihydrides...

Université de Neuchâtel

Photoemission of a Quantum Cavity with a Nonmagnetic Spin Separator

Koitzsch, Christian ; Battaglia, Corsin ; Clerc, Florian ; Despont, Laurent ; Garnier, Michael Bernard Gunnar ; Aebi, Philipp

In: Physical Review B, 2005, vol. 95, no. 126401, p. 1-4

Quantum well states are a consequence of confinement in a quantum cavity. In this study we investigate with photoemission the influence of the interface electronic structure on the quantum well state energy dispersion in ultrathin Mg(0001) films on W (110). Coupling between the sp-derived quantum well states and the substrate across the interface becomes manifest in a deviation from...

Université de Neuchâtel

Direct evidence for ferroelectric polar distortion in ultrathin lead titanate perovskite films

Despont, Laurent ; Koitzsch, Christian ; Clerc, Florian ; Aebi, Philipp ; Lichtensteiger, Céline ; Triscone, Jean-Marc ; Garcia de Abajo, F.J. ; Bousquet, E. ; Ghosez

In: Despont, Laurent ; Institut de Physique, Université de Neuchâtel, Switzerland, 2006, vol. 73, no. 094110, p. 1-6

X-ray photoelectron diffraction is used to directly probe the intracell polar atomic distortion and tetragonality associated with ferroelectricity in ultrathin epitaxial PbTiO3 films. Our measurements, combined with ab initio calculations, unambiguously demonstrate noncentrosymmetry in films a few unit cells thick, imply that films as thin as three unit cells still preserve a...

Université de Neuchâtel

Lattice-distortion-enhanced electron-phonon coupling and Fermi surface nesting in 1T-TaS2

Clerc, Florian ; Battaglia, Corsin ; Bovet, M ; Despont, Laurent ; Monney, Claude ; Cercellier, Hervé ; Garnier, Michael Bernard Gunnar ; Aebi, Philipp ; Berger, Helmuth ; Forró, László

In: Physical Review B, 2006, vol. 74, no. 155114, p. 1-7

The temperature dependence of the electronic structure of the quasi-two-dimensional material 1T-TaS2 is revisited by considering angle-resolved photoemission spectroscopy (ARPES) and density functional theory to calculate the imaginary part of the static electronic susceptibility characterizing the nesting strength. While nesting appears to play a role in the high temperature...

Université de Neuchâtel

Fermi-surface-induced lattice distortion in NbTe2

Battaglia, Corsin ; Cercellier, Hervé ; Clerc, Florian ; Despont, Laurent ; Garnier, Michael Gunnar ; Koitzsch, Christian ; Aebi, Philipp ; Berger, Helmuth ; Forró, László ; Ambrosch-Draxl, Claudia

In: Physical Review B, 2005, vol. 72, no. 195114, p. 1-10

The origin of the monoclinic distortion and domain formation in the quasi-two-dimensional layer compound NbTe2 is investigated. Angle-resolved photoemission shows that the Fermi surface is pseudogapped over large portions of the Brillouin zone. Ab initio calculation of the electron and phonon band structure as well as the static RPA susceptibility lead us to conclude that Fermi...

Université de Neuchâtel

Evidence for an Excitonic Insulator Phase in 1T–TaS2

Cercellier, H. ; Monney, Claude ; Clerc, F. ; Battaglia, Corsin ; Despont, Laurent ; Garnier, Michael Bernard Gunnar ; Beck, H. ; Aebi, Philipp ; Patthey, L. ; Berger, H. ; Forró, L.

In: Physical Review Letters, 2007, vol. 99, no. 146403, p. 1-4

We present a new high-resolution angle-resolved photoemission study of 1T–TaS2 in both its room-temperature, normal phase and its low-temperature, charge-density wave phase. At low temperature the photoemission spectra are strongly modified, with large band renormalizations at high-symmetry points of the Brillouin zone and a very large transfer of spectral weight to backfolded...

Université de Neuchâtel

Multiple scattering investigation of the 1T-TaS2 surface termination

Despont, Laurent ; Clerc, F. ; Garnier, Michael Bernard Gunnar ; Berger, H. ; Forró, L. ; Aebi, Philipp

In: The European Physical Journal B - Condensed Matter and Complex Systems, 2006, vol. 52, no. 3, p. 421-426

Multiple scattering theory based on a cluster model is used to simulate full hemispherical X-ray photoelectron diffraction measurements on a 1T-TaS2 (0001) surface. Key points to determine the surface termination are discussed. As the commonly applied single scattering simulations do not give satisfying results, a multiple scattering approach has to be used to accurately...

Université de Neuchâtel

X-ray photoelectron diffraction study of ultrathin PbTiO3 films

Despont, Laurent ; Lichtensteiger, Céline ; Clerc, F. ; Garnier, Michael Bernard Gunnar ; Garcia de Abajo, F.J. ; Van Hove, M. A. ; Triscone, Jean-Marc ; Aebi, Philipp

In: European Physical Journal B (The) - Condensed Matter and Complex Systems, 2006, vol. 49, no. 2, p. 141-146

Full hemispherical X-ray photoelectron diffraction (XPD) experiments have been performed to investigate at the atomic level ultrathin epitaxial c-axis oriented PbTiO3 (PTO) films grown on Nb-doped SrTiO3 substrates. Comparison between experiment and theory allows us to identify a preferential ferroelectric polarization state in a 60 Å -thick PTO film. Multiple scattering...