DISCLAIMERThis report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information. apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise docs not necessarily constitute or imply its endorsement, m m - A key difference between a d-wave and an anisotropic s-wavc superconductor is the expected effect of nomagnetic point defects on YE, T, of the former becomes zero whereas To of the latter attains a nonzero constant value beyond B critical concentration of impurities. We report the first observation that T, of an YBCO single crystal beconies zero after 4.1% of the planar oxygens 0(2,3) are displaced by 4OOkeV electron irradiation along the c-axis. Our data therefore indicate that YBCO is ti d-wave superconductor. We also report evidence of a disorder-induced superconductor-to-normal-metal transition.

by a Contrauor of the US. Government under contract No. W-31-109-ENG-38. Aaordingiy. the U.S. Oovernmenl retain8 a nonexclusive. royalty-lree Ikanse to Wish or reproduce the published lorm of thm contr0utbn. or albw DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thsreof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracj, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

We report results of a study of electron tunneling into bulk samples of the new high-T, superconductor Y-Ba-Cu-0 using point-contact tunneling. Based on a superconductive tunneling interpretation, the results show exceptionally large energy gaps in these materials (roughly 24=100 meV), implying 2hlkaT, -13. Similar values were found previously by us for La-Sr-Cu-O. We also see structure in the I-V curves similar to that seen in La-Sr-Cu-O. On the basis of the asymmetries observed in the I-V characteristics, we believe that the natural tunneling barrier on this material is of the Schottky type.

In-situ weak-beam observations of the development of electron irradiation damage at dislocations in silver are described. Dislocations constrict and promote in their vicinity the formation of stacking-fault tetrahedra. The possibility that these are of interstitial nature is discussed. p882. defects and J Takamura,

No abstract