Lu doping in Yb3Rh4Ge13 reveales Kondo behavior at low Yb concentrations (after the superconductivity in the pure Lu compound is suppressed), followed by intermediate valence bahavior for x > 0.3.
Intermediate Valence Systems
The hybridization of transition metal or rare earth localized d or f electrons with conduction electrons often gives rise to exotic electronic properties such as intermediate valence states, Kondo insulator, pseudogap, superconductivity, heavy fermion or quantum criticality. Intermediate valence states generally form with electronically unstable rare earths like Ce, Yb, Eu and Sm. The f electron levels in such systems are close to the s-d band favoring an intermediate valence state, in which case the rare earth ions often fluctuate between two electronic configurations competing for stability. We are particularly interested in Yb based compounds, for which the two competing electronic states are the nearly degenerate 4f13 (magnetic) and 4f14 (nonmagnetic) states. An intermediate valence (IV) state occurs in these compounds when the difference in their Fermi energy EF and the 4f energy level Ef is comparable to the width of the hybridized 4f level.
Binod K. Rai, Iain W. H. Oswald, Julia Y. Chan, and E. Morosan, "Intermediate valence to heavy fermion through a quantum phase transition in Yb3(Rh1−xTx)4Ge13 (T = Co, Ir) single crystals" Phys. Rev. B 93,035101 (2016)
Binod K. Rai, Iain W. H. Oswald, Jiakui K. Wang, Gregory T. McCandless, Julia Y. Chan, and E. Morosan, "Superconductivity in Single Crystals of Lu3T4Ge13–x (T = Co, Rh, Os) and Y3T4Ge13–x (T = Ir, Rh, Os)" Chem. Mater. 27, 2488 (2015)
B. K. Rai, and Emilia Morosan, "Intermediate valence in single crystals of (Lu1−x Y b x )3Rh4Ge13 (0 ≤ x ≤ 1)" APL Mat. 3, 041511 (2015)
Lu doping in Yb3Rh4Ge13 reveales Kondo behavior at low Yb concentrations (after the superconductivity in the pure Lu compound is suppressed), followed by intermediate valence behavior for x > 0.3.
Transition metal doping in Yb3Rh4Ge13 results in intermediate valence behavior in Yb3(Rh1−xTx)4Ge13 for T = Co and 0 < x < 1, while T = Ir doping drives the system into a heavy fermion state with a quantum critical point and non-Fermi liquid behavior around x = 0.5.