Dimensional crossover in the upper critical field of layered superconductors

Using the recently introduced ${\mathit{g}}_3$ model for layered superconductors, we calculate the angular and temperature dependence of the upper critical field ${\mathit{H}}_{\mathit{c}2}$. By lowering the temperature we find a crossover from three-dimensional bulk behavior to decoupled two-dimensional layers in both the temperature and angular dependence of ${\mathit{H}}_{\mathit{c}2}$. This behavior is remarkably consistent with recent experiments and the comparison with the measured angular dependence provides an estimate for the interlayer coupling ${\mathit{g}}_3$.