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

Abstract

We report the far-infrared transmission of the high-$T_c$ superconductor ${\mathrm{La}}_{1.8}$ ${\mathrm{Sr}}_{0.2}$ ${\mathrm{CuO}}_4$ at temperatures above and below $T_c$ 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 ${\mathrm{cm}}^{\mathrm{-}2}$ (i.e., 72 K).