Field-dependent cyclotron mass of CeAl2

We have studied the cyclotron mass of the heavy fermion compound CeAl2 by m easuring the de Haas-van Alphen effect in pulsed magnetic fields up to 52 T and at temperatures down to 1.7 K. With the field parallel to [1 1 1] we f ind two high-frequency extremal orbits with frequencies of 6.40 and 5.41 kT . These values are close to those reported in the literature for the same h eld orientation. We observe a striking held dependence of the cyclotron mas s of the 6.40 kT orbit, similar to the mass decrease observed in CeB6. The cyclotron mass changes from m*/m(e) = (4.4 +/- 0.7) at 35 T to m*/m(e) = (2 .0 +/- 1.1) at 49 T. This should be compared with the value m*/m(e) = (14.7 +/- 0.5) reported below 13 T. (C) 1999 Elsevier Science B.V. All rights re served.