THE TRANSITION TO SUPERCONDUCTIVITY IN 2-DIMENSIONAL SYSTEMS UNDER STRONG MAGNETIC-FIELDS

Two-Dimensional electron systems are unique in their response to stron g magnetic fields in both the normal and the superconducting states. I n addition to the complete quantization of the single electron orbits and energy spectrum, the effective cyclotron mass can be varied contin uously over a large range by tilting the external field with respect t o the axis of the cylindrical Fermi surface, thus leading to the possi bility of zero spin splittings, quenched Pauli pair breaking, and reso nant Cooper-pairing. We discuss the nature of the magnetic response, a ssociated with these effects, near the transition to extremely type-II superconductivity at low temperatures. The magnetisation oscillations crossover smoothly from the normal to the superconducting regime as t he field is lowered across H(c2)(T). In contrast to the usual dHvA osc illations pattern, the amplitude of the oscillations' envelop is shown to increase with the decreasing field below H(c2)(T), up to a maximum located at lower fields for lower temperatures. Under the conditions of sero spin splitting the system may crossover into a new (reentrant) superconducting state, driven by the resonant pairing of many electro ns within a single Landau level.