Publications de Marco Grioni | EPFL Graph Search

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We measured the momentum dependence of magnetic excitations in the model spin-1/2 2D antiferromagnetic insulator Sr2CuO2Cl2 (SCOC). We identify a single-spin-wave feature and a multimagnon continuum, with different polarization dependences. The spin waves ...

We have exploited angle-resolved photoelectron spectroscopy to study changes in the quasiparticle excitations of CuO2 planes as a function of the carrier density, in optimally doped and underdoped Bi2Sr2CaCuO8+x and in Sr2CuO2Cl2. We have observed large changes in the E versus k dispersion of the quasiparticle bands, and in the topology of the Fermi surface away from optimal doping. We have also found that the carrier density has a nontrivial effect on the symmetry properties of these states.

We report results of an angle-resolved high-resolution photoemission study of strongly overdoped Bi2Sr2CaCu2O8+x single crystals with T-c similar to 60 K. We find a nonzero superconducting (SC) gap along all three high symmetry directions in the Brillouin zone, in contrast with a d-wave scenario of high temperature superconductivity. Our data indicate that both the maximum gap value and the gap anisotropy decrease with overdoping. (C) 1999 Elsevier Science B.V. All rights reserved.

We report angle-resolved photoemission (ARPES) measurements, density functional and model tight-binding calculations on Ba2IrO4 (Ba-214), an antiferromagnetic (T-N = 230 K) insulator. Ba-214 does not exhibit the rotational distortion of the IrO6 octahedra that is present in its sister compound Sr2IrO4 (Sr-214), and is therefore an attractive reference material to study the electronic structure of layered iridates. We find that the band structures of Ba-214 and Sr214 are qualitatively similar, hinting at the

In nodal-line semimetals, linearly dispersing states form Dirac loops in the reciprocal space with a high degree of electron-hole symmetry and a reduced density of states near the Fermi level. The result is reduced electronic screening and enhanced correla ...

We used X-ray absorption in the partial fluorescence yield mode (PFY-XAS), and resonant X-ray emission (RXES) to study the pressure dependence of Yb valence in the intermediate valence compound YbAl2. We find that the Yb valence changes from 2.25 at ambient pressure to 2.95 at 385 kbar, and that the valence transition is completed around 200 kbar. The combined use of complementary spectroscopic techniques considerably reduces the uncertainties in the extracted valence values. (C) 2004 Elsevier B.V. All righ

We have determined the effective attenuation length of photoelectrons over the range of kinetic energies from 4 to 6 keV in Co, Cu, Ge, and Gd2O3. The intensity of the substrate (Si) and overlayer core level peaks was measured as a function of the thicknes ...

New temperature-dependent angle resolved photoemission (ARPES) data on the quasi-one-dimensional Peierls compound (TaSe4)(2)I suggest a new interpretation of the spectral lineshapes, which removes discrepancies with the transport and thermodynamic results. We argue that the carriers are heavily dressed by the interaction with the lattice, and that the ARPES spectra are dominated by incoherent features. Signatures of the Peierls transitions are observed at the correct energy scale, but only with vanishingly

High-resolution resonant inelastic x-ray scattering (RIXS) at the oxygen K edge has been used to study the orbital excitations of Ca2RuO4 and Sr2RuO4. In combination with linear dichroism x-ray absorption spectroscopy, the ruthenium 4d-orbital occupation and excitations were probed through their hybridization with the oxygen p orbitals. These results are described within a minimal model, taking into account crystal field splitting and a spin-orbit coupling λso=200 meV. The effects of spin-orbit interaction

We briefly review some recent photoelectron spectroscopy (PES) studies of quasi one- and two-dimensional metallic systems. We discuss the spectral features of a metallic system, the expected fingerprints of the metal-insulator transition and some experimental and conceptual limitations of the single particle framework. This approach gives a satisfactory interpretation of PES experiments in 2D charge-density-wave materials. The single particle picture is however incompatible with experiments on 1D systems.

Chirality in tellurium arises from a Peierls distortion driven by strong electron-phonon coupling, making this material a unique candidate for observing a light-induced topological phase transition. Using time- and angle-resolved photoelectron spectroscopy ...

We have exploited angle-resolved photoelectron spectroscopy (ARPES) to study the electronic structure of single crystal samples of high T-c material Bi2Sr2CaCu2O8+delta and of the antiferromagnetic insulator Sr2CuO2Cl2. As one moves away from optimal doping into underdoped region (T-c as low as 30K), the large Fermi surface sheet centered around the (pi,pi) point evolves into a small pocket centered around (pi/2,pi/2), and the saddle-point van Hove singularity is lost This evolution can be extrapolated to S

Random defects destroy long-range phase coherence, and inhibit the metal-insulator transition in the charge density wave (CDW) system 1T-TaS2. Photoelectron spectroscopy with high resolution reveals corresponding changes in the electronic structure. Core level spectra indicate a temperature-dependent limited growth of commensurate CDW domains. Screening by free carriers from the domain boundaries reduces the Coulomb repulsion in the Ta d band by similar to 1/3, compared to pure samples, yielding a finite sp

We have studied by high resolution angle resolved photoelectron spectroscopy the spectral properties of two metallic and one insulating Bechgaard salts, quasi-1D organic materials. The spectra of the metals show no dispersing quasiparticle peak crossing the Fermi level. Instead a deep pseudogap is observed. The spectral lineshape is incompatible with that of ''normal'' metals. The spectrum of the insulator exhibits a real energy gap.

We investigate the composition and temperature (10-450 K) dependence of the Yb valence in YbMn6Ge6-xSnx (x = 0.0, 3.8, 4.2, 4.4, and 5.5) using resonant inelastic x-ray scattering (RIXS). The observed change in the Yb valence with composition (from v simil ...

Resonant inelastic x-ray scattering in the soft x-ray regime has been profiting much from technical advances that have lowered considerably the instrumental linewidth. At the ADRESS beam line of the Swiss Light Source the SAXES spectrometer can be used to ...

We performed high-resolution angle resolved photoelectron spectroscopy studies of quasi-one-dimensional organic materials. For TTF-TCNQ, we observe dispersive spectral features corresponding to the donor and acceptor band. For the Bechgaard salts (TMTSF)(2)X and (TMTTF)(2)X, on the other hand, we observe a non-dispersive band feature. In all casts thr photoelectron spectrum is strongly renormalized at the chemical potential, in contrast with the common picture of a normal metal. (C) 1999 Elsevier Science B.

The reflectivity of TmS single crystals has been measured between 3 meV and 12 eV at room temperature and at 6 K, Besides 3p(6)-5d interband transitions a plasma edge due to free carriers is observed. In the middle infrared (near 50 meV) two sharp lines are found which are interpreted as transitions from the Fermi level into empty crystal field split 4f(1 3) states. A Bremsstrahlen isochromat spectroscopy (BIS) measurement supports the assumption that the empty 4f(1 3) state is close to the Fermi energy. (C

V L-3 edge resonant inelastic x-ray scattering measurements performed on high quality BaVS3 single crystals reveal that the intra-t(2g) dd excitations close to the elastic peak are suppressed below the metal-insulator transition induced by the Peierls inst ...

We exploited angle-resolved photoelectron spectroscopy (ARPES) with high energy resolution to map the band structure of the typical one-dimensional organic conductor TTF-TCNQ. We directly observe dispersing spectral features corresponding to the donor (TTF) and acceptor (TCNQ) bands, and their crossing at the Fermi wavevector k(F). Near the chemical potential, however, the quasiparticle peak are completely renormalized away, and the spectrum is totally incoherent. The suggest that we have observed the dispe

Marco Grioni

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Measurement of Magnetic Excitations in the Two-Dimensional Antiferromagnetic Sr2CuO2Cl2 Insulator Using Resonant X-Ray Scattering: Evidence for Extended Interactions

Doping effects on the electronic structure of CuO2 planes

The symmetry of the order parameter in highly overdoped Bi2Sr2CaCu2O8+x

The electronic structure of the high-symmetry perovskite iridate Ba2IrO4

Light-Induced Renormalization of the Dirac Quasiparticles in the Nodal-Line Semimetal ZrSiSe

Valence changes in YbAl2 under pressure: a resonant inelastic X-ray emission study

Quantifying the effective attenuation length in high-energy photoemission experiments

Evidence for strong correlations in a 1D Peierls system

Spin-orbit-induced orbital excitations in Sr2RuO4 and Ca2RuO4: A resonant inelastic x-ray scattering study

Photoemission in low-dimensional systems

Light-induced renormalization of the band structure of chiral tellurium

Doping dependence of the Fermi surface in the cuprates: A photoemission investigation

Spectral consequences of broken phase coherence in 1T-TaS2

Unusual spectral signatures of organic 1D metals

Composition and temperature dependence of the Yb valence in YbMn6Ge6-xSnx studied by RIXS

Crystal field and low energy excitations measured by high resolution RIXS at the L-3 edge of Cu, Ni and Mn

Experimental spectral signatures of organic 1D metals

Empty 4f states in TmS

Opening of a Peierls gap in BaVS3 probed by V L-3 edge resonant inelastic x-ray scattering

Experimental electronic structure of a 1D organic metal: TTF-TCNQ