Gap symmetry and intrinsic intraplane pinning of untwinned YBa₂Cu₃O₇ single crystals

Abstract

The interplane (cb) and intraplane (ab) anisotropy of untwinned YBa₂ Cu₃0₇ single crystals has been investigated by means of the torque magnetometry. To extract the reversible and irreversible components, the torque was measured as a function of increasing angle as well as decreasing angle. The interplane irreversible torque Γ_irr shows two-fold peaks at θ_c =90 ° and270 ° (of half width11 ° at77 K) due to the well-known intrinsic interplane pinning. A novel intrinsic pinning has been discovered in the intraplane irreversible torque, i.e., Γ_irr shows four-fold peaks of half width20° at77 K when θ_a =0 °, 90 °, 180 ° and270 °. We argue that the intrinsic intraplane pinning comes from the four-fold nature of the gap parameter.