ORDER-PARAMETER SYMMETRY OF HIGH-T_cSUPERCONDUCTORS BY MEANS OF BULK PHYSICAL QUANTITY

本文用体物理量研究了高温超导体的序参量对称性。这与许多基于表面性质进行的实验相反。我们使用分裂型6-T超导磁体建立了一个新的扭矩磁力计。非孪晶YBa_2Cu_3O_7单晶的面内扭矩由二重对称性和四重对称性组成。前者来自于m_a和m_B之间的质量各向异性。后者与序参量对称性有关，与现有理论一致。我们的结果与d_对称性不相容<xy>，但与d_&lt;x^2-y^2&gt;对称性符合得很好.我们认为我们的发现是令人信服的，因为磁矩反映了整个晶体的信息。

The order parameter symmetry of high-T_0 superconductors has been investigated by means of the bulk physical quantity. This is in contrast with that many experiments were carried out on the basis of surface properties. We built a new torque magnetometer using a split-type 6-T superconducting magnet. The measurement program has been coded using HP-BASIC.The in-plane torque of an untwinned YBa_2Cu_3O_7 single crystal consists of two-fold and four-fold symmetries. The former comes from the mass anisotropy between m_a and m_b. The latter is related with the order parameter symmetry, and is consistent with the existing theories. Our results are not compatible with the d_<xy> symmetry but are in good accordance with the d_<x^2-y^2> symmetry. We consider that our findings are convincing because the magnetic torque reflects information over the whole crystal.