Thermal Signatures of the Kondo Volume Collapse in Cerium

Abstract

X-ray diffraction measurements of cerium in the vicinity of the isostructural gamma-alpha transition have been performed with high precision and accuracy from room temperature to almost 800 K. The disputed location of the critical point has been found to occur at 1.5+/-0.1 GPa and 480+/-10 K. The data are well fit by the Kondo volume collapse model plus a quasiharmonic representation of the phonons. The resultant free energy is validated against data for the thermodynamic Grüneisen parameter and, beyond the dominant spin-fluctuation contribution, indicates a dramatic change in the lattice Grüneisen parameter across the transition.

Heavy fermion superconductor CeCu2Si2under high pressure: Multiprobing the valence crossover

“…The error bars take into account the uncertainty on p and that introduced via ρ 0 (mentioned above). A simple fit of the type ∝ (T − T cr ) −γ yields T CeCu 2 Si 2 cr ∼ = −8 ± 3K and γ ∼ = 1 and a similar treatment of the Ce data 11 T Ce cr ∼ = 465 K (in agreement with more recent data 5 ). Notice that experimental limitations like sample imperfections or the inevitable p gradient tend to broaden the resistivity drop, and hence the extracted T cr may be slightly underestimated.…”

“…3 and 12). Its value is more than one order of magnitude higher than at p = 0 and roughly corresponds to half of the giant N measured in CeCoIn 5 . 61 In addition, N (T ) exhibits a maximum around 2 K for p < 5 GPa and independent of H , most likely revealing a characteristic energy scale (Fig.…”

“…1), the first-order valence transition (FOVT) line (γ -α transition), the location of its critical end point (CEP), and the valence crossover (VCO) line have been unambiguously identified by several experiments. 5,11 In CeCu 2 Si 2 , obviously the CEP lies at much lower T , where the electron delocalization is accompanied in the transport data by a decrease in resistivity, in combination with SC at the lowest T . Preceding experiments point toward distinct natures of the two superconducting (sc) phases 7,9 (related to p c and p V , respectively) and have unveiled close to p V features peculiar to the concept of critical VF, such as a T -linear resistivity and an increased residual resistivity ρ 0 .…”

Core and shallow-cored- tof-shell excitations in rare-earth metals

“…Alloying (chemical substitution), pressure, and temperature can effectively tune the 4f electron localization, turning the eigenstates of the system into admixtures of atomic-like states with corresponding admixtures of f-electron occupancy. In particular, Ce, Pr, and Nd metals exhibit a trend of pressure-driven volume collapses-from large (Ce, 15%) to moderate (Pr, 9%) to none at all (Nd)-related to 4f electron delocalization [3,6,[8][9][10][11][12][13][14][15][16][17][18][19]. The character of this delocalization may be substantially different in each material, and the xray scattering used here promises to be an important probe for relevant high-pressure work.…”

“…Not coincidentally, these applications often critically depend on the novel properties of the rare earth 4f electrons, properties that are derived primarily from their anisotropic spatial profile and ability to transform between localized and itinerant behavior. The mechanism responsible for 4f electron delocalization is contested [1][2][3][4][5][6][7] However, the borderline between atomic and collective behavior in rare earth metals is often thin, even nearby these seemingly simple cases. Alloying (chemical substitution), pressure, and temperature can effectively tune the 4f electron localization, turning the eigenstates of the system into admixtures of atomic-like states with corresponding admixtures of f-electron occupancy.…”