HEAVY FERMION BEHAVIOR IN EXTREMELY LOW CARRIER CONCENTRATION SYSTEM YB4AS3

We have investigated the series of Yb pnictides with anti-Th3P4 structure. The valence of Yb varies from about 2 of Yb4Bi3 to 2.25 of Yb4As3 with the decreasing weight of the pnictogen. In the case of Yb4As3, the 4f 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/Yb3+ion. Yb4As3 is a new heavy Fermion compound which inquires whether the heavy Fermion state needs free carriers. © 1990, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.