Role of Valence Fluctuations in the Superconductivity of Ce122 Compounds

Abstract

Pressure dependence of the Ce valence in CeCu(2)Ge(2) has been measured up to 24 GPa at 300 K and to 17 GPa at 18-20 K using x-ray absorption spectroscopy in the partial fluorescence yield. A smooth increase of the Ce valence with pressure is observed across the two superconducting (SC) regions without any noticeable irregularity. The chemical pressure dependence of the Ce valence was also measured in Ce(Cu(1-x)Ni(x))(2)Si(2) at 20 K. A very weak, monotonic increase of the valence with x was observed, without any significant change in the two SC regions. Within experimental uncertainties, our results show no evidence for the valence transition with an abrupt change in the valence state near the SC II region, challenging the valence-fluctuation mediated superconductivity model in these compounds at high pressure and low temperature.

Magnetic, thermal, and electronic-transport properties of EuMg2Bi2 single crystals

“…Rare-earth-based intermetallic compounds have been of significant interest for many years due to their complex properties such as superconductivity, heavy fermion behavior, valence fluctuations, giant magnetocaloric effect, Kondo behavior, and quantum criticality [23][24][25][26][27][28][29][30][31][32][33][34][35][36]. Several rare-earth-based intermetallic compounds have also been discovered recently to exhibit topological states coupled with magnetic interactions [37][38][39][40][41][42][43].…”

Origin of Pressure-induced Superconducting Phase in KxFe2−ySe2 studied by Synchrotron X-ray Diffraction and Spectroscopy

“…We also performed the bulk sensitive x-ray absorption (XAS) measurements with partial fluorescence (PFY) mode at the Fe K absorption edge27. We have used the PFY-XAS method where a decay process with shorter life time is selected, resulting spectra are narrower, and making fine electronic structure near the absorption edge better visible272829. Our results show the change in the c -axis compressibility around boundary pressure of the SC I and SC II phases, suggesting a crystal structure change at this pressure, probably a tetragonal (T) to collapsed tetragonal (cT) transition.…”

Intermediate valence in single crystals of (Lu1−xY bx)3Rh4Ge13 (0 ≤ x ≤ 1)

“…Two competing energy scales, the Ruderman-Kittel-Kasuya-Yosida (RKKY) T RKKY ∝ (J N(E F )) 2 and the Kondo energy T K ∝ e −1/J N (E F ) (where J is the spin coupling constant and N(E F ) is the density of states at the Fermi level), give rise to either Kondo, HF, or HF superconducting behavior when T K ≫ T RKKY , or magnetic when T RKKY ≫ T K . [12][13][14][15][16] A crossover from Kondo lattice or HF to an intermediate valence state has been observed in a number of Kondo lattice or HF compounds, such as doped CeCu 2 Si 2 , 17 CePtSi, 18 or under pressure in YbCu 4 Ag, 19 CeCu 6 , 20 and CeBe 13 . 21 In this study, a continuous solid solution (Lu 1−x Yb x ) 3 Rh 4 Ge 13 displays a continuous evolution from superconductivity in a disordered metal close to x = 0 (Ref.…”