DIMENSIONAL CROSSOVER OF WEAK-LOCALIZATION IN A MAGNETIC-FIELD

We study the dimensional crossover of weak localization in strongly an isotropic systems. This crossover from three-dimensional behavior to a n effective lower-dimensional system is triggered by increasing temper ature if the phase coherence length gets shorter than the lattice spac ing a. A similar effect occurs in a magnetic field if the magnetic len gth L-m becomes shorter than a(D-parallel to/D-perpendicular to)(gamma ), where D-parallel to/D-perpendicular to is the ratio of the diffusio n coefficients parallel and perpendicular to the planes or chains. gam ma depends on the direction of the magnetic field, e.g., gamma=1/4 or 1/2 for a magnetic field parallel or perpendicular to the planes in a quasi-two-dimensional system. We show that even in the limit of large magnetic field, weak localization is not fully suppressed in a lattice system. Experimental implications are discussed in detail. [S0163-182 9(97)06841-0].