## CMT63

##
The Nonlinear Meissner Effect in Unconventional Superconductors

**Author(s):**
D. Xu, S.-K. Yip and J. A. Sauls

**Comments:** 30 pages with 16 figures

**Journal:**

Physical Review B, 51, 16233 (1995)
[DOI]

**Abstract:**

We examine the long-wavelength
current response in anisotropic superconductors and show how the field-dependence
of the Meissner penetration length can be used to detect the structure
of the order parameter. Nodes in the excitation gap lead to a nonlinear
current-velocity constitutive equation at low temperatures which is distinct
for each symmetry class of the order parameter. The effective Meissner
penetration length is linear in *H* and exhibits a characteristic
anisotropy for fields in the *ab*-plane that is determined by the
positions of the nodes in momentum space. The nonlinear current-velocity
relation also leads to an intrinsic magnetic torque for in-plane fields
that are not parallel to a nodal or antinodal direction. The torque scales
as *H*^{3} for
*T -> 0* and has a characteristic angular
dependence. We analyze the effects of thermal excitations, impurity scattering
and geometry on the current response of a
*d*_{x}^{2}_{-y}^{2}superconductor,
and discuss our results in light of recent measurements of the low-temperature
penetration length and in-plane magnetization of single-crystals of
YBa_{2}Cu_{3}O_{7-y}
and LuBa_{2}Cu_{3}O_{7-y}.