ANISOTROPY OF UPPER CRITICAL-FIELD IN THE (110)T AND (001)T PLANES FOR SINGLE-CRYSTAL LA1.86SR0.14CUO4

Anisotropy of the upper critical field HC2 has been investigated in detail for single-crystal La1.86Sr0.14CuO4 grown by the TSFZ method. When magnetic fields are applied in the (110)t plane, large anisotropy of Hc2, H⊥c2/H″c2 ≳ 10, is observed and the angular dependence is well expressed by the effective mass model suitable for anisotropic 3-dimensional superconductors. When magnetic fields are applied in the (001)t plane, namely in the CuO2 plane, small but clear anisotropy of Hc2 with 4-fold symmetry is found. This is not attributed to the anisotropy of Hc2 or the critical current due to the twin structure in the orthorhombic phase, but seems due to the anisotropy originating in the electronic state in the CuO2 plane. © 1990, Elsevier Science Publishers B.V. (North-Holland). All rights reserved.