- Binod Rai, Rice University, Houston, Texas
Rare earth compounds show many interesting electronic properties such as superconductivity, magnetism, and heavy fermion behavior. One of the interesting features, especially in Ce- and Yb-based compounds, is Kondo behavior, which gives rise to exotic ground states due to strong hybridization of the f-electrons with the conduction electrons. While many heavy fermion compounds based on Ce are known, the number of known Yb heavy fermions is substantially smaller. In the quest for understanding Kondo behavior in Yb-based systems, I discovered 25 rare earth–based compounds within two families: R3T4Ge13 and RT3M7 (R = Y, Ce, Gd-Lu, T = Co, Rh, Ir, and M = Ge, Si), which had previously been poorly explored. The discoveries include the first 3 Kondo systems in the 1-3-7 family along with 7 (Y,Lu)3T4Ge13 superconductors and low-carrier density systems. Very few 4f low-carrier Kondo semimetal systems had been reported, where metallic resistivity behavior was found in their nonmagnetic analogues. In this talk, I will show evidence for low carrier behavior both in a Kondo system Yb3Ir4Ge13 and its nonmagnetic counterpart Lu3Ir4Ge13. Furthermore, a fragile magnetic state occurs in the Yb compound below 0.9 K, which can be suppressed to zero temperature through substitution of Lu for Yb. The second part of my talk includes a discussion of metamagnetism in the antiferromagnetic heavy fermion YbRh3Si7, which shows magnetic order below TN = 7.5 K with moments lying within the ab plane.