MAGNETORESISTANCE AND DE HAAS-VAN-ALPHEN EFFECT IN YRU2SI2

We have measured the magnetoresistance and the de Haas-van Alphen effe ct of YRu2Si2. The Fermi surface and cyclotron mass of YRu2Si2 are com pared to those of LaRu2Si2 and LaRu2Ge2. Main hole Fermi surfaces of t he three compounds are similar and ellipsoidal in shape, which occupy about half of the Brillouin zone. The small hole Fermi surface with a shape of rugby ball is one in number for YRu2Si2, while three for LaRu 2Si2 and LaRu2Ge2. A cylindrical Fermi surface and a multiply-connecte d Fermi surface exist for YRu2Si2, while there exists a doughnut like electron Fermi surface for LaRu2Si2 and LaRu2Ge2. The cyclotron masses of YRu2Si2 are about 50% and 10% larger than those of LaRu2Si2 and La Ru2Ge2, respectively.