Abstract
The reversible magnetic torque of untwinned YBa2Cu3O7 single crystals shows the four-fold symmetry in thea-b plane. The irreversible torque indicates evidence for a novel intrinsic pinning along thea andb axes. These facts mean that the free energy of the four-fold symmetry has a minimum when the field is applied along thea orb axis. The results are consistent with those expected from thed x 2−y 2 symmetry and rule out the possibility of thed xy symmetry. The Fermi surface anisotropy is not responsible for the observed anisotropy. This is firstbulk evidence for thek-dependent gap anisotropy on the Fermi surface. The two-fold anisotropy parameter is found as\(\gamma _{ab} = \sqrt {{{m_a } \mathord{\left/ {\vphantom {{m_a } {m_b }}} \right. \kern-\nulldelimiterspace} {m_b }}} = 1.18 \pm 0.14\).
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Ishida, T., Okuda, K., Asaoka, H. et al. In-plane torque and gap symmetry of untwinned YBa2Cu3O7 crystals. Czech J Phys 46 (Suppl 3), 1217–1218 (1996). https://doi.org/10.1007/BF02562723
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DOI: https://doi.org/10.1007/BF02562723