Angular dependence of the penetration depth in unconventional superconductors - art. no. 014501

We examine the Meissner state nonlinear electrodynamic effects on the field and angular dependence of the low-temperature penetration depth lambda of superconductors in several kinds of unconventional pairing states. with nod es or deep minima ("quasinodes") in the energy gap. Our calculations are pr ompted by the fact that, for typical unconventional superconducting materia l parameters, the predicted size of these effects for lambda exceeds the av ailable experimental precision for this quantity by a much larger factor th an for others. We obtain expressions for the nonlinear component of the pen etration depth Delta lambda for different two- and three-dimensional nodal or quasinodal structures. Each case has a characteristic signature as to it s dependence on the size and orientation of the applied magnetic held. This shows that Delta lambda measurements can be used to elucidate the nodal or quasinodal structure of the energy gap. For nodal lines we find that Delta lambda is linear in the applied held, while the dependence is quadratic fo r point nodes, For layered materials with YBa2Cu3O7-delta type anisotropy, our results for the angular dependence of Delta lambda differ greatly from those for tetragonal materials and are in agreement with experiment. For th e two- and three-dimensional quasinodal cases, Delta lambda is no longer pr oportional to a power of the held and the field and angular dependences are not separable, with a suppression of the overall signal as the node is fil led in.