Exploring Heavy Fermion Materials near a Quantum Critical Point
- Author(s): Jang, Sooyoung;
- et al.
Results for two categories of heavy fermion systems : (1) a new type of non-centrosymmetric heavy fermion system R₂TM₁₂Pn₇ (R = rare earth, TM = transition metal, Pn = P, As), and (2) Yb substitution in CeCoIn₅, which is a heavy fermion superconductor, Ce₁-xYbxCoIn₅, are described. The phenomena seen in the system R₂TM₁₂Pn₇ are discussed in terms of strong hybridization between the localized f- electron states and the conduction electron states, such as a crossover between Fermi liquid and non-Fermi liquid behavior in Yb₂Ni₁₂P₇, or the presence of a large value of the Sommerfeld coefficient, [gamma] ̃ 650 mJ/mol Sm K² in Sm₂Ni₁₂P₇. The extraordinary electronic phenomena found in the system Ce₁-xYbxCoIn₅ include Yb valence fluctuations, a change in the Fermi surface topology, and suppression of the quantum critical field occurring at a nominal concentration of x ̃ 0.2. However, the suppression of the superconducting critical temperature with nominal Yb concentration x for bulk single crystals is much weaker than that observed in thin film samples. The actual Yb composition of bulk single crystals is found to be about 1 /3 of the nominal concentration, resolving the discrepancy between the variation of the physical properties of Ce₁- xYbxCoIn₅ single crystals and thin films with Yb concentrations