Low-temperature resistivity of La0.7Sr0.3MnO3 ultra thin films: Role of quantum interference effects

The low-temperature (< 60 K) transport properties of as-grown La0.7Sr0.3MnO3 ultrathin films, deposited by the molecular beam epitaxy, have been investigated as a function of the sample thickness (from 40 to 3.5 nm) and in the presence of an external magnetic field. With decreasing thickness, a clear low-temperature resistivity minimum slightly affected by the application of the magnetic field has been observed, and its presence has been possibly interpreted in terms of quantum interference effects. As a function of the thickness, a crossover from a three-dimensional (3D) to a two-dimensional (2D) behavior of the system takes place below 20 nm. A re-entrant 3D behavior is induced in ultrathin films by the application of large (>20 kOe) magnetic fields. Negative values of the magnetoresistance have been observed in all of the investigated samples for all of the measured magnetic fields.