Using a flux technique we have grown crystals of YBa2Cu3O7 which are superconducting above 90 K as-grown. In 10% of these crystals large orthorhombic single domains exceeding 100×100 μm2 are observed using polarised light. The conductivity anisotropy (≈100 at 290 K to ≈300 near Tc) indicates a strikingly two-dimensional electronic state. Anisotropy in the thermopower is also reported. Tunneling into these crystals provides direct evidence that the electronic spectrum is different from the BCS spectrum. A (possibly) novel spin-dependent gap which scales linearly with field is described. Finally, paraconductivity studies on crystals with transition widths δT ≈ 0.2 K are summarised.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering