A Monte Carlo study on distribution of CuO chains in YBa 2Cu 3O 6+2 c

Abstract

Distribution of CuO chains in YBa 2Cu 3O 6+2 c , with respect to different chain lengths, has been studied in terms of the two dimensional asymmetric next-nearest-neighbor Ising (ASYNNNI) model, for the case of orthorhombic-I structural phase. If p( l) stands for the fraction of CuO chains of length l ( l equals to number of oxygen atoms that are linked in the chain), the results obtained show that p( l) decreases monotonically with l, very accurately fitting to p( l) = AB l , as at very low temperatures so at a very high temperatures as well (ranking from ≈300 K to 1800 K), and at all values of oxygen concentration c. Both parameters A and B were found to depend on ( c, T) only through a single quantity—the average length l av( c, T) of CuO chains in the system. The expressions for A( l av) = A( l av( c, T)) and B( l av) = B( l av ( c, T)), that were derived out of extensive Monte Carlo (MC) numerical simulations on the chain probability distribution p( l) and independently obtained values of l av were found to be very accurately fulfilled at all calculated points of ( c, T) space. The particular behavior of p( l) dependance has been assigned to 1 d Ising model type of oxygen atom fluctuations along cooper mediated V 2 < 0 bonds (i.e., along b crystallographic axes). The importance of knowing the exact form of p( l), for evaluation of the number of transferred electronic holes from CuO chains to superconducting CuO 2 layers, has been discussed together with its possible impact on the two-plateaus shape of T c( c) dependance.