Université de Fribourg

Selective probing of hidden spin-polarized states in inversion-symmetric bulk ${\mathrm{MoS}}_{2}$

Razzoli, Elia ; Jaouen, Thomas ; Mottas, Marie-Laure ; Hildebrand, Baptiste ; Monney, Gaël ; Pisoni, A. ; Muff, S. ; Fanciulli, M. ; Plumb, N. C. ; Rogalev, V. A. ; Strocov, V. N. ; Mesot, Joël ; Shi, Ming ; Dil, J. H. ; Beck, Hans ; Aebi, Philipp

In: Physical Review Letters, 2017, vol. 118, no. 8, p. 086402

Spin- and angle-resolved photoemission spectroscopy is used to reveal that a large spin polarization is observable in the bulk centrosymmetric transition metal dichalcogenide MoS2. It is found that the measured spin polarization can be reversed by changing the handedness of incident circularly polarized light. Calculations based on a three-step model of photoemission show that the valley and...

Université de Fribourg

Short-range phase coherence and origin of the $1T-{\mathrm{TiSe}}_{2}$ charge density wave

Hildebrand, Baptiste ; Jaouen, Thomas ; Didiot, Clément ; Razzoli, Elia ; Monney, Gaël ; Mottas, Marie-Laure ; Ubaldini, A. ; Berger, Helmuth ; Barreteau, C. ; Beck, Hans ; Bowler, D. R. ; Aebi, Philipp

In: Physical Review B, 2016, vol. 93, no. 12, p. 125140

The impact of variable Ti self-doping on the 1T−TiSe2 charge density wave (CDW) is studied by scanning tunneling microscopy. Supported by density functional theory, we show that agglomeration of intercalated-Ti atoms acts as preferential nucleation centers for the CDW that breaks up in phase-shifted CDW domains whose size directly depends on the intercalated-Ti concentration and which are...

Université de Fribourg

Excitonic Josephson effect in double-layer graphene junctions

Zenker, B. ; Fehske, H. ; Beck, Hans

In: Physical Review B, 2015, vol. 92, no. 8, p. 081111

We show that double-layer graphene (DLG), where an external potential induces a charge imbalance between n- and p-type layers, is a promising candidate to realize an exciton condensate in equilibrium. To prove this phenomenon experimentally, we suggest coupling two DLG systems, separated by a thin insulating barrier, and measuring the excitonic Josephson effect. For this purpose we calculate the...

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

Fate of the excitonic insulator in the presence of phonons

Zenker, B. ; Fehske, H. ; Beck, Hans

In: Physical Review B, 2014, vol. 90, no. 19, p. 195118

The influence of phonons on the formation of the excitonic insulator has hardly been analyzed so far. Recent experiments on Ta2NiSe5,1T−TiSe2, and TmSe0.45Te0.55, being candidates for realizing the excitonic-insulator state, suggest, however, that the underlying lattice plays a significant role. Employing the Kadanoff-Baym approach we address this issue theoretically. We show that owing to the...

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...

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

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

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

Monney, Claude ; Schwier, E. F. ; Garnier, Michael G. ; Battaglia, C. ; Mariotti, N. ; Didiot, C. ; 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...