DEHAAS-VANALPHEN OSCILLATIONS IN EXTREMELY TYPE-II NEARLY 2D SUPERCONDUCTORS

Two-Dimensional (2D) electron systems are expected to exhibit striking ly new phenomena in the superconducting state when placed under strong quantizing magnetic fields. We analyze the nature of the field depend ent magnetization around the normal-superconducting phase boundary at low temperatures. Under ideal conditions (i.e. for sufficiently weak e lectron scattering by sideorder) both the normal and the superconducti ng components of the magnetization are in the 2D quantum diamagnetic r egime, i.e. both are purely oscillatory and of the same order of magni tude. Unlike the normal 2D magnetooscillations, however, which are gen erated only by the two Landau levels adjacent to the Fermi energy, the superconducting ones involve many Landau levels around the Fermi ener gy and have a gapless structure. In contrast to the usual dHvA oscilla tions pattern, the amplitude of the oscillations' envelop is shown to increase with the decreasing field below H(c2)(T), up to a maximum loc ated at lower fields for lower Temperatures. Under the conditions of z ero spin splitting the system may crossover into a new (reentrant) sup erconducting state, driven by the (resonant) pairing of many electrons within a single Landau level.