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Harmonium is a vacuum ultraviolet (VUV) photon source built within the Lausanne Centre for Ultrafast Science (LACUS). Utilising high harmonic generation, photons from 20-110 eV are available to conduct steady-state or ultrafast photoelectron and photoion s ...

We exploited complementary synchrotron radiation spectroscopies to study the Yb 4f electronic configuration in three representative intermediate-valence materials: YbAl3, YbInCu4, and YbCu2Si2. High-resolution x-ray absorption (PFY-XAS), resonant inelastic ...

We performed optical and photoemission experiments on the Bechgaard salt (TMTSF)(2)ReO4, a quasi-one-dimensional (1D) organic conductor that undergoes a metal-insulator (Peierls) transition at T-c similar to 180 K. As in other compounds of the same family, we observe non-Ferri liquid features in the metallic state, namely a deep pseudogap at the chemical potential. A fully gapped state develops below T-c from this peculiar normal state. Across the transition we successively observe, on the same material, th

Using angle-resolved photoemission spectroscopy, we probe the electronic band structure of TaTe4 single crystal samples. Resistivity and optical measurements were also performed on the same samples. The experimental data indicate a combination of quasi-one-dimensional and three-dimensional electronic properties. We observe a finite spectral intensity, but no dispersing quasiparticle states near the chemical potential. [S0163-1829(99)06611-4].

When a Mott metal-insulator transition is inhibited by a small amount of disorder in the layered dichalcogenide 1T-TaS2, an inhomogeneous superconducting state arises below T=2.1 K and coexists with a nearly commensurate charge-density wave. By angle-resol ...

We performed angle-resolved photoelectron spectroscopy (ARPES) and resistivity measurements on the layered metal 1T-TiTe2. We determined the quasiparticle dispersion and lifetime. In particular, we could characterize and separately evaluate the effects of the electron-electron and electron-phonon interactions on the experimental spectra. The good correlation between transport and spectroscopic scattering rates indicates that this material behaves as a model Fermi liquid system.

We report on the temperature dependence of the ZrTe5 electronic properties, studied at equilibrium and out of equilibrium, by means of time and angle resolved photoelectron spectroscopy. Our results unveil the dependence of the electronic band structure ac ...

We discuss the spectral signatures of strong electronic correlations and electron-phonon interactions in two representative low-dimensional systems. In the 2D compound 1T-TaSe2 a charge-density-wave (CDW) induces a narrowing of the conduction band, which triggers a surface metal-insulator (M-I) transition and the disappearance of the quasiparticle (QP) features. In the 1D blue bronze K0.3MoO3 strong interaction with the lattice lead to pseudogapped polaronic lineshapes, and the large mass renormalization ma

We investigate the evolution of both the occupied and unoccupied electronic structure in representative compounds of the infinitely adaptive superlattice series (Sb2)m−Sb2Te3 (m=0–3) by means of angle-resolved photoemission spectroscopy and time-delayed tw ...

High-resolution angle-resolved (ARPES) photoemission in the quasi-one dimensional (1D) Peierls systems (TaSe4)(2)I and K0.3MoO3 reveals spectral features with clear 1D character. Their dispersion and polarization dependence is consistent with open Fermi surfaces and with the symmetry properties of the lattice. However the measured spectral lineshapes are unusual in various respects, as shown also by a comparison with the quasiparticle spectra of a 'good' metal. A consistent description of the normal metalli

We review some recent spectroscopic results on low-dimensional systems, including high-T-c superconductors, and charge density wave compounds. We briefly discuss the reasons for the present interest in these materials, and the relevance of band mapping experiments by angle-resolved photoemission spectroscopy. The main focus of the paper is on high-energy resolution, which can be exploited to probe the quasiparticle excitations, and to study the characteristic instabilities of the Fermi surface. Gap spectros

We measured, by angle-resolved photoemission spectroscopy, the electronic structure of LiCu2O2, a mixed-valence cuprate where planes of Cu(I) (3d(10)) ions are sandwiched between layers containing one-dimensional edge-sharing Cu(II) (3d(9)) chains. We find ...

The low-temperature microscopic magnetic properties of the quasi-2D heavy-fermion compound, CePt2In7 are investigated by using a positive muon-spin rotation and relaxation (mu+SR) technique. Clear evidence for the formation of a commensurate antiferromagne ...

Collective modes are responsible for the emergence of novel quantum phases in topological materials. In the quasi-one dimensional (1D) Weyl semimetal (TaSe4)(2)I < i , a charge density wave (CDW) opens band gaps at the Weyl points, thus turning the system ...

We have carried out high-resolution photoemission experiments on two quasi-one-dimensional compounds: K0.3MoO3 and (TaSe4)2I. In both systems, a metal-insulator transition associated with a lattice distortion is reported. We show that the Fermi-step characteristic of a metallic phase is not observed above the Peierls temperature. As this Fermi step is always observed in higher-dimensional metals, we propose that this behavior results from the singular properties of one-dimensional systems and we suggest dif

Disorder has a strong influence on the spectral properties of the Bi2Sr2CaCu2O8+x high-T-c superconductor, both in the normal and in the superconducting state. High-resolution photoemission reveals a progressive quasiparticle suppression with increasing disorder in electron-irradiated optimally doped single crystals. The spectral Line shapes of the disordered samples show striking analogies with those of underdoped samples specifically the widely discussed pseudogap at the chemical potential. Disorder provi

When electrons are subject to a potential with two incommensurate periods, translational invariance is lost, and no periodic band structure is expected. However, model calculations based on nearly free one-dimensional electrons and experimental results from high-resolution photoemission spectroscopy on a quasi-one-dimensional material do show dispersing band states with signatures of both periodicities. Apparent band structures are generated by the nonuniform distribution of electronic spectral weight over

High-resolution angle-resolved photoemission spectroscopy (ARPES) on the quasi-one-dimensional Peierls system K0.3MoO3 reveals a "hidden" open Fermi surface and band features displaying the symmetry properties of the underlying lattice. However, the ARPES line shapes and optical data suggest that the corresponding quasiparticles are heavily renormalized by strong electron-phonon interactions. The temperature dependence of the leading edge of the mostly incoherent spectrum bears signatures of the Peierls tra

We have irradiated by thermal neutrons single crystals of the Bi-2212 high T-c superconductor. The irradiated samples are insulators, but they regain high T-c superconductivity after an annealing in He at 450-550 degrees C. Depending on irradiation doses and annealing parameters, we obtained two insulators, with more or less disorder, and two superconductors with different values of T-c. We performed resistivity, a.c. susceptibility and angle resolved photoemission studies (ARPES). The coherent quasiparticl

High-resolution x-ray absorption measurements reveal a rare-earth-dependent splitting of the Ni K edge in the insulating, charge-disproportionated state of the whole RNiO3 perovskite family. The splitting is five times larger for LuNiO3 [2.5(1) eV] than fo ...

Marco Grioni

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Harmonium: An Ultrafast Vacuum Ultraviolet Facility

Comparison of bulk-sensitive spectroscopic probes of Yb valence in Kondo systems

The transition from a pseudogapped metal to an insulator: photoemission and optics of (TMTSF)(2)ReO4

Coexisting one-dimensional and three-dimensional spectral signatures in TaTe4

Superconducting phase in the layered dichalcogenide 1T-TaS_{2} upon inhibition of the metal-insulator transition

Quasiparticle scattering processes in a model Fermi liquid: 1T-TiTe2

Ultrafast Optical Control of the Electronic Properties of ZrTe5

Strong electron-electron and electron-phonon interactions in one- and two-dimensional solids

Engineering the topological surface states in the (Sb2)m−Sb2Te3(m=0–3) superlattice serie

Band features and strong correlations in 1D Peierls systems

High-resolution photoemission in low-dimensional conductors and superconductors

Electronic Phase Separation and Dramatic Inverse Band Renormalization in the Mixed-Valence Cuprate LiCu2O2

Magnetic order in the 2D Heavy-Fermion system CePt2In7 studied by mu+SR

Optically induced changes in the band structure of the Weyl charge-density-wave compound (TaSe4)(2)I

Unusual Photoemission Spectral-Function Of Quasi-One-Dimensional Metals

Alternative pseudogap scenario: Spectroscopic analogies between underdoped and disordered Bi2Sr2CaCu2O8+x

Electronic structure of solids with competing periodic potentials

Mobile small polarons and the Peierls transition in the quasi-one-dimensional conductor K0.3MoO3

The effect of deliberately induced disorder on the electronic structure of the Bi-2212 high T-c superconductor

Charge disproportionation in RNiO3 perovskites (R=rare earth) from high-resolution x-ray absorption spectroscopy