Heavy Fermions in YbAl ₃ Studied by the de Haas-van Alphen Effect

The carried out the de Haas-van Alphen (dHvA) experiment in YbAl3 with the cubic crystal structure. One of the six dHvA branches, named beta with a dHvA frequency of 4.5 x 10(7) Oe, is nearly spherical in topology and has a large cyclotron mass of 23.9 m(0). The other branches were observed only in small angular regions centered at symmetrical directions. Their cyclotron masses are in the range from 13.5 to 17.4 m(0). The topology of the Fermi surface cannot be explained by the conventional band model because the fully occupied 4f-levels in YbAl3 are below the Fermi level. A small alteration so as to shift upwards the 4f levels is necessary to fit to the experimental dHvA data. These give a direct evidence that the 4f-electrons form heavy fermions at low temperatures, which is most likely related to the many-body Kondo effect.