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Université de Fribourg

Time- and angle-resolved photoemission spectroscopy of solids in the extreme ultraviolet at 500 kHz repetition rate

Puppin, M. ; Deng, Y. ; Nicholson, C. W. ; Feldl, J. ; Schröter, N. B. M. ; Vita, H. ; Kirchmann, P. S. ; Monney, Claude ; Rettig, L. ; Wolf, M. ; Ernstorfer, R.

In: Review of Scientific Instruments, 2019, vol. 90, no. 2, p. 023104

Time- and angle-resolved photoemission spectroscopy (trARPES) employing a 500 kHz extreme-ultraviolet light source operating at 21.7 eV probe photon energy is reported. Based on a high-power ytterbium laser, optical parametric chirped pulse amplification, and ultraviolet-driven high-harmonic generation, the light source produces an isolated high-harmonic with 110 meV bandwidth and a flux of...

Université de Fribourg

Coupled Cu and Mn charge and orbital orders in YBa₂Cu₃O₇/Nd 0.65 (Ca 1-y Sr y ) 0.35 MnO₃ multilayers

Perret, Edith ; Monney, Claude ; Johnston, S. ; Khmaladze, Jarji ; Lyzwa, Fryderyk ; Gaina, Roxana ; Dantz, M. ; Pelliciari, Jonathan ; Piamonteze, C. ; Mallett, B.P.P. ; Minola, M. ; Keimer, B. ; Schmitt, Thorsten ; Bernhard, Christian

In: Communications Physics, 2018, vol. 1, no. 1, p. 45

The observation of a charge density wave in the underdoped cuprate high Tc superconductors (Cu-CDW) raised a debate about its relationship with superconductivity. In bulk YBa2Cu3O7−δ the Cu-CDW is incipient and mainly pinned by defects. Nevertheless, a large magnetic field can induce a true long-range Cu- CDW order as it suppresses superconductivity. An enhanced Cu-CDW order was also ...

Université de Fribourg

Inhibition of the photoinduced structural phase transition in the excitonic insulator ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$

Mor, Selene ; Herzog, Marc ; Noack, Johannes ; Katayama, Naoyuki ; Nohara, Minoru ; Takagi, Hide ; Trunschke, Annette ; Mizokawa, Takashi ; Monney, Claude ; Stähler, Julia

In: Physical Review B, 2018, vol. 97, no. 11, p. 115154

Femtosecond time-resolved midinfrared reflectivity is used to investigate the electron and phonon dynamics occurring at the direct band gap of the excitonic insulator Ta2NiSe5 below the critical temperature of its structural phase transition. We find that the phonon dynamics show a strong coupling to the excitation of free carriers at the Γ point of the Brillouin zone. The optical response...

Université de Fribourg

Robustness of the charge-ordered phases in ${\mathrm{IrTe}}_{2}$ against photoexcitation

Monney, Claude ; Schuler, A. ; Jaouen, T. ; Mottas, Marie-Laure ; Wolf, Thomas ; Merz, M. ; Muntwiler, Matthias ; Castiglioni, L. ; Aebi, Philipp ; Weber, F. ; Hengsberger, M.

In: Physical Review B, 2018, vol. 97, no. 7, p. 075110

We present a time-resolved angle-resolved photoelectron spectroscopy study of IrTe2, which undergoes two first-order structural and charge-ordered phase transitions on cooling below 270 K and below 180 K. The possibility of inducing a phase transition by photoexcitation with near-infrared femtosecond pulses is investigated in the charge-ordered phases. We observe changes of the spectral...

Université de Fribourg

Ultrafast electronic band gap control in an excitonic insulator

Mor, Selene ; Herzog, Marc ; Golež, Denis ; Werner, Philipp ; Eckstein, Martin ; Katayama, Naoyuki ; Nohara, Minoru ; Takagi, Hide ; Mizokawa, Takashi ; Monney, Claude ; Stähler, Julia

In: Physical Review Letters, 2017, vol. 119, no. 8, p. 086401

We report on the nonequilibrium dynamics of the electronic structure of the layered semiconductor Ta2NiSe5 investigated by time- and angle-resolved photoelectron spectroscopy. We show that below the critical excitation density of FC=0.2 mJ cm−2, the band gap narrows transiently, while it is enhanced above FC. Hartree-Fock calculations reveal that this effect can be explained by the presence...

Université de Fribourg

Three-dimensional momentum-resolved electronic structure of $1T\text{-}{\mathrm{TiSe}}_{2}:$ A combined soft-x-ray photoemission and density functional theory study

Vydrova, Z. ; Schwier, Eike Fabian ; Monney, Gaël ; Jaouen, Thomas ; Razzoli, Elia ; Monney, Claude ; Hildebrand, Baptiste ; Didiot, Clément ; Berger, Helmuth ; Schmitt, T. ; Strocov, V. N. ; Vanini, F. ; Aebi, Philipp

In: Physical Review B, 2015, vol. 91, no. 23, p. 235129

1T−TiSe2 is a quasi-two-dimensional transition metal dichalcogenide, which exhibits a charge density wave transition at a critical temperature of ∼200 K as well as low-temperature superconductivity induced by pressure or intercalation. The electronic energy dispersion measured by soft x-ray angle-resolved photoemission is not only momentum resolved parallel to the surface but also...

Université de Fribourg

Quasi one-dimensional Ag nanostructures on Si(331)–(12 × 1)

Mariotti, Nicolas ; Didiot, Clément ; Schwier, E. F. ; Monney, Claude ; Battaglia, Corsin ; Aebi, Philipp

In: Surface Science, 2015, vol. 639, p. 39–42

We report on the deposition of sub-monolayer Ag on the Si(331)–(12 × 1) surface. The growth of one-dimensional Ag nanostructures is observed by means of low-temperature scanning tunneling microscopy and low energy electron diffraction. We find that the deposited Ag is organized in nanostructures consistently taking “sawtooth” shapes. While the structures are not perfectly organized, their...

Université de Fribourg

Impact of electron-hole correlations on the $1T\text{-}{\mathrm{TiSe}}_{2}$ electronic structure

Monney, Gaël ; Monney, Claude ; Hildebrand, B. ; Aebi, Philipp ; Beck, Hans

In: Physical Review Letters, 2015, vol. 114, no. 8, p. 086402

Several experiments have been performed on 1T−TiSe2 in order to identify whether the electronic structure is semimetallic or semiconducting without reaching a consensus. In this Letter, we theoretically study the impact of electron-hole and electron-phonon correlations on the bare semimetallic and semiconducting electronic structure. The resulting electron spectral functions provide a direct...

Université de Fribourg

Chiral charge order in 1T-TiSe₂: Importance of lattice degrees of freedom

Zenker, B. ; Fehske, H. ; Beck, Hans ; Monney, Claude ; Bishop, A. R.

In: Physical Review B, 2013, vol. 88, no. 7, p. 075138

We address the question of the origin of the recently discovered chiral property of the charge-density-wave phase in 1T-TiSe₂, which so far lacks a microscopic understanding. We argue that the lattice degrees of freedom seem to be crucial for this novel phenomenon. We motivate a theoretical model that takes into account one valence and three conduction bands, a strongly screened Coulomb...

Université de Fribourg

Electron-hole fluctuation phase in 1T-TiSe₂

Monney, Claude ; Monney, Gaël ; Aebi, Philipp ; Beck, Hans

In: Physical Review B - Condensed Matter and Materials Physics, 2012, vol. 85, no. 23, p. 235150

To address the fluctuation regime above the critical temperature of the charge-density-wave phase of 1T-TiSe₂, we perform calculations using the Bethe-Salpeter equation for treating strong electron-hole correlations. Calculated photoemission intensity maps are in good agreement with the measured ones and provide a deeper understanding of the phase transition in terms of an electronic...