arXiv subjects

Jean-Pascal Rueff

Publications and source records attributed to Jean-Pascal Rueff.

25 records · Page 2Linked to original sources

arXiv2013

Unified understanding of the valence transition in the rare-earth monochalcogenides under pressure

Valence instability is a key ingredient of the unusual properties of f electron materials, yet a clear understanding is lacking as it involves a complex interplay between f electrons and conduc- tion states. Here we propose a unified picture of pressure-induced valence transition in Sm and Yb monochalcogenides, considered as model system for mixed valent 4f-electron materials. Using high-resolution x-ray absorption spectroscopy, we show that the valence transition is driven by the promotion of a 4f electron specifically into the lowest unoccupied (LU) 5d t2g band. We demonstrate with a promotional model that the nature of the transition at low pressures is intimately related to the density of states of the LU band, while at high pressures it is governed by the hybridization strength. These results set a new standard for the generic understanding of valence fluctuations in f-electron materials.

cond-mat.str-el↗

arXiv2012

Valence Instability of YbCu$_2$Si$_2$ through its quantum critical point

We report Resonant inelastic x-ray scattering measurements (RIXS) in YbCu$_2$Si$_2$ at the Yb L$_{3}$ edge under high pressure (up to 22 GPa) and at low temperatures (down to 7 K) with emphasis on the vicinity of the transition to a magnetic ordered state. We find a continuous valence change towards the trivalent state with increasing pressure but with a pronounced change of slope close to the critical pressure. Even at 22 GPa the Yb$^{+3}$ state is not fully achieved. The pressure where this feature is observed decreases as the temperature is reduced to 9 GPa at 7K, a value close to the critical pressure (\itshape{p\normalfont{$_c$}}\normalfont $\approx$ 7.5 GPa) where magnetic order occurs. The decrease in the valence with decreasing temperature previously reported at ambient pressure is confirmed and is found to be enhanced at higher pressures. We also compare the f electron occupancy between YbCu$_2$Si$_2$ and its Ce-counterpart, CeCu$_2$Si$_2$.

cond-mat.str-el↗

arXiv2009

Inelastic X-ray Scattering by Electronic Excitations in Solids at High Pressure

Investigating electronic structure and excitations under extreme conditions gives access to a rich variety of phenomena. High pressure typically induces behavior such as magnetic collapse and the insulator-metal transition in 3d transition metals compounds, valence fluctuations or Kondo-like characteristics in $f$-electron systems, and coordination and bonding changes in molecular solids and glasses. This article reviews research concerning electronic excitations in materials under extreme conditions using inelastic x-ray scattering (IXS). IXS is a spectroscopic probe of choice for this study because of its chemical and orbital selectivity and the richness of information it provides. Being an all-photon technique, IXS has a penetration depth compatible with high pressure requirements. Electronic transitions under pressure in 3d transition metals compounds and $f$-electron systems, most of them strongly correlated, are reviewed. Implications for geophysics are mentioned. Since the incident X-ray energy can easily be tuned to absorption edges, resonant IXS, often employed, is discussed at length. Finally studies involving local structure changes and electronic transitions under pressure in materials containing light elements are briefly reviewed.

cond-mat.str-el↗

arXiv2006

Probing the gamma-alpha Transition in Bulk Ce under Pressure: A Direct Investigation by Resonant Inelastic X-ray Scattering

We report on the most complete investigation to date of the 4f-electron properties at the gamma-alpha transition in elemental Ce by resonant inelastic x-ray scattering (RIXS). The Ce 2p3d-RIXS spectra were measured directly in the bulk material as a function of pressure through the transition. The spectra were simulated within the Anderson impurity model. The occupation number nf was derived from the calculations in both gamma- and alpha-phases in the ground state along with the f doubleoccupancy. We find that the electronic structure changes result mainly from band formation of 4f electrons which concurs with reduced electron correlation and increased Kondo screening at high pressure.

cond-mat.str-el↗

arXiv2006

Evidence for non-conventional pairing in Na$\_x$CoO$\_2$$\cdot$yH$\_2$O

We report on first investigation of the lattice dynamics in the novel superconducting material Na$\_{0.35}$CoO$\_2$$\cdot$1.3H$\_2$O and the non-hydrated parent compound Na$\_{0.7}$CoO$\_2$ by inelastic x-ray scattering. The measured phonon dispersion along the $Γ-M$ direction show a marked softening with hole doping of two optical phonon branches close to the Brillouin zone boundary. The phonon spectra, dispersion, and softening are well reproduced by first-principle calculations. The calculations indicates that the soft branches are mainly composed of Co-vibration modes. The estimation of the critical temperature based on electron-phonon coupling mechanism undisputedly points to a non-conventional superconducting state in this material.

cond-mat.str-el↗

arXiv2005

Temperature and pressure-induced spin-state transitions in LaCoO3

We report the continuous variation of the spin moment of cobalt in LaCoO3 across its temperature and pressure-induced spin transitions evidenced with Kβemission spectra. The first thermal transition is best described by a transition to an orbitally nondegenerate intermediate spin (S=1) state. In parallel, continuous redistribution of the 3d electrons is also indicated by partial fluorescence yield X-ray absorption spectra. At high pressure, our study confirms that the material becomes low spin between 40 and 70 kbar at room temperature.

cond-mat.str-el↗

arXiv1999

Pressure induced high-spin to low-spin transition in FeS evidenced by x-ray emission spectroscopy

We report the observation of the pressure-induced high-spin to low-spin transition in FeS using new high-pressure synchrotron x-ray emission spectroscopy techniques. The transition is evidenced by the disappearance of the low-energy satellite in the Fe K$β$ emission spectrum of FeS. Moreover, the phase transition is reversible and closely related to the structural phase transition from a manganese phosphide-like phase to a monoclinic phase. The study opens new opportunities for investigating the electronic properties of materials under pressure.

cond-mat.mtrl-sci↗