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

Spin–orbit splitting in the valence bands of 1T-TaS2 and 1T-TaSe2

Clerc, F. ; Bovet, M. ; Berger, H. ; Despont, Laurent ; Koitzsch, C. ; Gallus, O ; Patthey, L ; Shi, M. ; Krempasky, J. ; Garnier, Michael Bernard Gunnar ; Aebi, Philipp

In: Journal of Physics : Condensed Matter, 2004, vol. 16, p. 3271-3278

We perform angle-resolved photoemission spectroscopy on 1T-TaS2 and 1T-TaSe2 using synchrotron radiation. We observe a characteristic splitting of the chalcogen p-derived valence bands along high symmetry directions. Density functional theory calculation and group theory strongly suggest that this splitting is due to spin–orbit interaction along one...

Université de Neuchâtel

Fermi surface of layered compounds and bulk charge density wave systems

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

In: Journal of Physics : Condensed Matter, 2007, vol. 19, no. 355002, p. 1-17

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 function mapping despite its surface sensitivity. Discussed are TaS2, TaSe2, NbTe2, TiSe2 and...

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

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

Probing nanoscale ferroelectricity by photoelectron diffraction

Despont, Laurent ; Aebi, Philippe (Dir.)

Thèse de doctorat : Université de Neuchâtel, 2007 ; 1942.

This thesis is based on research carried out at the Institut de Physique, Université de Neuchâtel, Switzerland during the period 2003 - 2007, in collaboration with the DPMC, University of Geneva, where the samples have been grown. A ferroelectric is generally defined as a material with two or more stable states of different non-zero intrinsic lattice polarization which can be reversed through...

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...

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

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...