Heavy Fermion Behavior in Extremely Low Carrier Concentration System Yb4As3

We have investigated the series of Yb pnictides with anti-Th 3 P 4 structure. The valence of Yb varies from about 2 of Yb 4 Bi 3 to 2.25 of Yb 4 As 3 with the decreasing weight of the pnictogen. In the case of Yb 4 As 3 , the 4 f level is located around the band gap and the charge ordering below about 300 K has been observed. Further, in such a situation, we have observed a clear dense Kondo or heavy Fermion behavior in the resistivity, the magnetic susceptibility and the specific heat though the carrier concentration at 4.2 K is only about 0.001/Yb 3+ ion. Yb 4 As 3 is a new heavy Fermion compound which inquires whether the heavy Fermion state needs free carriers.