Absence of nonlinear meissner effect in (formula presented)

Abstract

We present measurements of the field and temperature dependence of the penetration depth (Formula presented) in high purity, untwinned single crystals of (Formula presented) in all three crystallographic directions. The temperature dependence of (Formula presented) is linear down to low temperatures, showing that our crystals are extremely clean. Both the magnitude and temperature dependence of the field dependent correction to (Formula presented) however, are considerably different from that predicted from the theory of the nonlinear Meissner effect for a d-wave superconductor (Yip-Sauls theory). Our results suggest that the Yip-Sauls effect is either absent or is unobservably small in the Meissner state of (Formula presented) © 1999 The American Physical Society.