Percolation nature of the 60-K to 90-K phase transition in YBa _2Cu_3O_(6+δ)

摘要

The temperature dependence of the heat capacity of the HTSC YBa _2Cu_3O_(6+δ) is measured in the temperature range 1.8-300 K and the doping range 0.70 < δ < 0.86. The results obtained suggest that the transition from the 60-K to the 90-K phase in YBa _2Cu_3O_(6+δ) has a percolation nature and that the underdoped 60-K phase represents a heterophase structure in which numerous superconducting clusters are embedded into an insulating matrix.