Cylindrical Fermi surfaces formed by a flat magnetic Brillouin zone in uranium dipnictides

We succeeded in growing high-quality single crystals of UX2 (X = Bi, Sb, As or P) by the self-flux and chemical transport methods and carried out de Haas-van Alphen and Shubnikov-de Haas experiments. We found quasi-two-dimensional Fermi surfaces in these U compounds. Fermi surfaces of UBi2 are found to consist of one spherical Fermi surface and two cylindrical Fermi surfaces. Each Fermi surface in UBi2 changes into two cylindrical surfaces in USb2 and UAs2. This change in the Fermi surfaces is well explained on the basis of a flat magnetic Brillouin zone. The quasi-two-dimensional character of the Fermi surfaces is mainly due to the conduction electrons in the U plane, including the 5f electrons. The itinerant nature of 5f electrons is reflected in the large cyclotron masses. The magnetic breakthrough (breakdown) phenomenon is also discussed for USb2.