Heavy Fermions in YbAl₃ Studied by the de Haas-van Alphen Effect

Abstract

We carried out the de Haas-van Alphen (dHvA) experiment in YbAl₃ with the cubic crystal structure. One of the six dHvA branches, named β with a dHvA frequency of 4.5×10⁷ Oe, is nearly spherical in topology and has a large cyclotron mass of 23.9 m₀. 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 m₀. 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.