Low-carrier Density and Fragile Magnetism in a Kondo Lattice System*

Known low-carrier Kondo systems evolve from metallic non-magnetic analogues, while a recent theoretical model for the dilute carrier Kondo limit predicts semimetallic behavior. Very few 4f low-carrier Kondo systems have been reported, mostly based on Ce. In this talk, I will show evidence for low-carrier Kondo behavior in Yb₃Ir₄Ge₁₃ with a low carrier background as illustrated by the non-magnetic analogue Lu₃Ir₄Ge₁₃. A fragile magnetic state occurs in the Yb compound at very low temperatures, which, together with the semimetalic behavior, can be understood within the framework of the dilute-carrier limit of a Kondo lattice model. An entirely new regime of the Kondo effect is discovered, where the fragile magnetism can also be tuned in a non-Fermi liquid fashion through Lu-for-Yb substitution.