Measurement of the energy gap of YBa2Cu3O7 using ac susceptibility

Abstract
The low-temperature value of the energy gap in YBa2 Cu3 O7 was determined by fitting the imaginary part of the ac susceptibility at T<0.5Tc. The fit yields a value of 2Δ0=440±10 K, or 2Δ0kBTc=5±0.2.