Abstract
Point contact measurements in oriented La2−xSrxCuO4 samples were performed using metal tips. The current-voltage curves measured along the CuO plane direction (ab) are characteristic of the Andreev reflection phenomenon. The superconducting energy gap in theab plane is determined, Δab = 6± 1 meV, with a possibility for the existence of a lower subgap in the plane. A lower limit for the Fermi velocity in the CuO planes is also set by the measurements;VF≥6×107 cm/sec, which is significantly higher than the average velocity obtained by band calculations. The results are discussed in the context of different models for superconductivity in the layered oxides. In particular, we raise the possibility of an anisotropic gap parameter which may indicate a nonstandards-wave pairing in La2−xSrxCuO4. A comparison with previous results obtained on YBa2Cu2O7−δ is made.
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