Université de Fribourg

Mapping of electron-Hole excitations in the charge-density-wave system 1T-TiSe2 using resonant inelastic x-ray scattering

Monney, Claude. ; Zhou, K. J. ; Cercellier, H. ; Vydrova, Z. ; Garnier, Michael G. ; Monney, G. ; Strocov, V. N. ; Berger, Helmuth ; Beck, Hans ; Schmitt, T. ; Aebi, Philipp

In: Physical Review Letters, 2012, vol. 109, p. 047401

In high-resolution resonant inelastic x-ray scattering at the Ti L edge of the charge-density-wave system 1T-TiSe₂, we observe sharp low energy loss peaks from electron-hole pair excitations developing at low temperature. These excitations are strongly dispersing as a function of the transferred momentum of light. We show that the unoccupied bands close to the Fermi level can effectively be...

Université de Fribourg

Ab initio many-body effects in TiSe₂: A possible excitonic insulator scenario from GW band-shape renormalization

Cazzaniga, M. ; Cercellier, H. ; Holzmann, M. ; Monney, Claude ; Aebi, Philipp ; Onida, Giovanni ; Olevano, V.

In: Physical Review B - Condensed matter and materials physics, 2012, vol. 85, no. 19, p. 195111

We present both theoretical ab-initio results within the Hedin's GW approximation and experimental angle-resolved photoemission and scanning tunneling spectroscopy measurements on TiSe₂. With respect to the density-functional Kohn-Sham metallic picture, the many-body GW self-energy leads to a ≈0.2-eV band-gap insulator consistent with our STS spectra at 5 K. The highest valence and the lowest...

Université de Fribourg

Influence of elastic scattering on the measurement of core-level binding energy dispersion in X-ray photoemission spectroscopy

Schwier, Eike Fabian ; Monney, Claude ; Mariotti, Nicholas ; Vydrovà, Z. ; García-Fernández, Mirian ; Didiot, Clément ; Garnier, Michael G. ; Aebi, Philipp

In: The European Physical Journal B - Condensed Matter And Complex Systems, 2011, vol. 81, no. 4, p. 399-403

We explore the interplay between the elastic scattering of photoelectrons and the surface core level shifts with regard to the determination of core level binding energies in Au(111) and Cu3Au(100). We find that an artificial shift is created in the binding energies of the Au 4f core levels, that exhibits a dependence on the emission angle, as well as on the spectral intensity of the core...

Université de Fribourg

Exciton Condensation Driving the Periodic Lattice Distortion of 1T-TiSe₂

Monney, Claude ; Battaglia, Corsin ; Cercellier, H. ; Aebi, Philipp ; Beck, Hans

In: Physical Review Letters, 2011, vol. 106, no. 10, p. 106404

We address the lattice deformation of 1T-TiSe₂ within the exciton condensate phase. We show that, at low temperature, condensed excitons influence the lattice through electron-phonon interaction. It is found that at zero temperature, in the exciton condensate phase of 1T-TiSe₂, this exciton condensate exerts a force on the lattice generating ionic displacements comparable in amplitude to what...

Université de Fribourg

Valence band structure of the Si(331)-(12 × 1) surface reconstruction

Battaglia, Corsin ; Schwier, Eike Fabian ; Monney, Claude ; Didiot, Clément ; Mariotti, Nicolas ; Gaál-Nagy, Katalin ; Onida, Giovanni ; Garnier, Michael Gunnar ; Aebi, Philipp

In: Journal of Physics: Condensed Matter, 2011, vol. 23, no. 13, p. 135003

Using angle-resolved photoelectron spectroscopy we investigate the electronic valence band structure of the Si(331)-(12 × 1) surface reconstruction for which we recently proposed a structural model containing silicon pentamers as elementary structural building blocks. We find that this surface, reported to be metallic in a previous study, shows a clear band gap at the Fermi energy, indicating...

Université de Fribourg

Dramatic effective mass reduction driven by a strong potential of competing periodicity

Monney, Claude ; Schwier, Eike Fabian ; Garnier, Michael G. ; Battaglia, C. ; Mariotti, N. ; Didiot, Clément ; Cercellier, H. ; Marcus, J. ; Berger, H. ; Titov, A. N. ; Beck, Hans ; Aebi, Philipp

In: Europhysics Letters, 2010, vol. 92, no. 4, p. 47003

We present angle-resolved photoemission experiments on 1T-TiSe₂ at temperatures ranging from 13 K to 288 K. The data evidence a dramatic renormalization of the conduction band below 100 K, whose origin can be related to the new potential responsible for the charge density wave phase at low temperature in this system. The renormalization translates into a substantial effective mass...

Université de Fribourg

Temperature-dependent photoemission on 1T-TiSe₂: Interpretation within the exciton condensate phase model

Monney, Claude ; Schwier, Eike Fabian ; Garnier, Michael G. ; Mariotti, Nicholas ; Didiot, Clément ; Beck, Hans ; Aebi, Philipp ; Cercellier, H. ; Marcus, J. ; Battaglia, C. ; Berger, H.

In: Physical Review B, 2010, vol. 81, no. 15, p. 1551104

The charge-density-wave phase transition of 1T-TiSe₂ is studied by angle-resolved photoemission over a wide temperature range. An important chemical-potential shift which strongly evolves with temperature is evidenced. In the framework of the exciton condensate phase, the detailed temperature dependence of the associated order parameter is extracted. Having a mean-field-like behavior at low...

Université de Fribourg

Structure and stability of the Si(331)-(12×1) surface reconstruction investigated with first-principles density functional theory

Battaglia, Corsin ; Onida, Giovanni ; Gaál-Nagy, Katalin ; Aebi, Philipp

In: Physical Review B: condensed matter and materials physics, 2009, vol. 80, no. 21, p. 214102

We recently proposed a structural model for the Si(331)-(12×1) surface reconstruction containing silicon pentamers and adatoms as elementary structural building blocks. Using first-principles density functional theory we here investigate the stability of a variety of adatom configurations and determine the lowest-energy configuration. We also present a detailed comparison of the energetics...

Université de Fribourg

Temperature dependence of the excitonic insulator phase model in 1T-TiSe₂

Monney, Claude ; Cercellier, H. ; Battaglia, Corsin ; Schwier, Eike Fabian ; Didiot, Clément ; Garnier, M.G. ; Beck, Hans ; Aebi, Philipp

In: Physica B: Condensed Matter, 2009, vol. 404, no. 19, p. 3172-3175

Recently, detailed calculations of the excitonic insulator phase model adapted to the case of 1T-TiSe2 have been presented. Through the spectral function theoretical photoemission intensity maps can be generated which are in very good agreement with experiment [H. Cercellier, et al., Phys. Rev. Lett. 99 (2007) 146403]. In this model, excitons condensate in a BCS-like manner and give rise to a...

Université de Fribourg

On the electronic impact of abnormal C4-bonding in N-heterocyclic carbene complexes

Heckenroth, Marion ; Neels, Antonia ; Garnier, Michael G. ; Aebi, Philipp ; Ehlers, Andreas W. ; Albrecht, Martin

In: Chemistry - A European Journal, 2009///doi: 10.1002/chem.200900249

Sterically similar palladium dicarbene complexes have been synthesized that comprise permethylated dicarbene ligands which bind the metal center either in a normal coordination mode via C2 or abnormally via C4. Due to the strong structural analogy of the complexes, differences in reactivity patterns may be attributed to the distinct electronic impact of normal versus abnormal carbene bonding,...