Relationship between conductivity and phase coherence length in cuprates

The large (10(2) - 10(5)) and strongly temperature dependent resistive anis otropy eta = (sigma(ab)/sigma(c))(1/2) of cuprates perhaps holds the key to understanding their normal state inplane sigma(ab) and out-of-plane sigma( c) conductivities. It can be shown that eta is determined by the ratio of t he phase coherence lengths l(i) in the respective directions: sigma(ab)/sig ma(c) = l(ab)(2)/l(c)(2). In layered crystals in which the out-of-plane tra nsport is incoherent, l(c) is fixed, equal to the interlayer spacing. As a result, the T-dependence of eta is determined by that of l(ab), and vice ve rse, the in-plane phase coherence length can be obtained directly by measur ing the resistive anisotropy. We present data for hole-doped YBa2Cu3Oy (6.3 < y < 6.9) and Y1-xPrxBa2Cu3O7-delta (0 < x less than or equal to 0.55) an d show that sigma(ab) of crystals with different doping levels can be well described by a two parameter universal function of the in-plane phase coher ence length. In the electron-doped Nd2-xCexCuO4-y, the dependence sigma(ab) (eta) indicates a crossover from incoherent to coherent transport in the c- direction.