Far-infrared measurement of the energy gap of La1.8Sr0.2CuO4

We report the far-infrared transmission of the high-Tc superconductor La1.8Sr0.2CuO4 at temperatures above and below Tc and for magnetic fields up to 10 T. At 7 K our data is best described by a distribution of superconducting energy gaps with a representative value of about 50 cm-2 (i.e., 72 K). © 1987 The American Physical Society.