RECENT ADVANCES IN RAISING T-C AND ESTABLISHING THE GAP-SYMMETRY OF HIGH-T-C CUPRATE SUPERCONDUCTORS

The most recent attempts in raising T-c of cuprate superconductors wer e successful by synthesizing new Hg-based cuprate materials. We discus s some properties of materials from this series with varying numbers o f Cu-O planes per unit cell, including the considerable rise of the cr itical temperature tinder the influence of external pressure. In the s econd part of this contribution, various attempts to directly determin e the symmetry of the superconducting order parameter of high-T-c, cup rates are mentioned and set into perspective. The experimental approac hes are all based on probing the phase of the order parameter in suita bly connected closed superconducting loops. The evidence for unconvent ional order-parameter symmetry an these materials is growing.