Universality class of the structural phase transition in the normal phase of cuprate superconductors

The tetragonal-orthorhombic structural phase transition of oxygen atoms in the basal plane of YBa2Cu3O6+delta high-T-C cuprate superconductors is studied numerically. By mapping the system onto the asymmetric next-nearest-neighbor Ising model, we characterize this phase transition. Results indicate the degrees of critical behavior. We show that this phase transition occurs at the temperature T-C similar or equal to 0.148 eV in the thermodynamic limit. By analyzing the critical exponents, it is found that this universality class displays some common features, with the two-dimensional three-state Potts model universality class, although the possibility of other universality classes cannot be ruled out. Conformal invariance at T = T-c is investigated using the Schramm-Loewner evolution (SLE) technique, and it is found that the SLE diffusivity parameter for this system is 3.34 +/- 0.01.