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...

Université de Neuchâtel

Electronic structure of ZrTe3

Starowicz, P. ; Battaglia, Corsin ; Clerc, F. ; Despont, Laurent ; Prodan, A. ; van Midden, H. J. P. ; Szerer, U. ; Szytuła, A. ; Garnier, Michael Bernard Gunnar ; Aebi, Philipp

In: Journal of Alloys and Compounds, 2007, vol. 442, no. 1-2, p. 268-271

The Fermi surface topology of the layered superconducting charge density wave compound ZrTe3 is investigated by angle resolved photoelectron spectroscopy and density functional theory. The Fermi surface is dominated by bands originating from two perpendicular systems of quasi one-dimensional chains. Nesting and opening of a pseudogap at temperatures as high as 250 K are signatures of a...

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

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

Structural investigations of epitaxial InN by x-ray photoelectron diffraction and x-ray diffraction

Hofstetter, Daniel ; Despont, Laurent ; Garnier, Michael Bernard Gunnar ; Baumann, Esther ; Giorgetta, Fabrizio R. ; Aebi, Philipp ; Kirste, Lutz ; Lu, Hai ; Schaff, William J.

In: Applied Physics Letters, 2007, vol. 90, no. 191912, p. 1-3

The authors investigated a 1 µm thick molecular beam epitaxy–grown InN film by means of full hemispherical x-ray photoelectron diffraction and high resolution x-ray diffraction. While x-ray diffraction reveals that this nominally hexagonal InN layer contains roughly 1% of cubic phase InN, a comparison between measured and simulated x-ray photoelectron diffraction data allowed them to...

Université de Neuchâtel

Monodomain to polydomain transition in ferroelectric PbTiO3 thin films with La0.67Sr0.33MnO3 electrodes

Lichtensteiger, Céline ; Dawber, Matthew ; Stucki, Nicolas ; Triscone, Jean-Marc ; Hoffman, Jason ; Yau, Jeng-Bang ; Ahn, Charles H. ; Despont, Laurent ; Aebi, Philipp

In: Applied Physics Letters, 2007, vol. 90, no. 052907, p. 1-3

Finite size effects in ferroelectric thin films have been probed in a series of epitaxial perovskite c-axis oriented PbTiO3 films grown on thin La0.67Sr0.33MnO3 epitaxial electrodes. The film thickness ranges from 480 down to 28 Å (seven unit cells). The evolution of the film tetragonality c/a, studied using high resolution x-ray diffraction...

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...