Order parameter symmetry: biaxial vs. twinned uniaxial nature of the Q1 super-lattice order

Determine whether the Q1 translational symmetry breaking with Q=(δ1,0,0) observed in PrBa2Cu3O7 and partially Pr-substituted YBa2Cu3O7 corresponds to a biaxial order or to a twinned uniaxial order, by resolving the order parameter symmetry beyond current diffraction limitations.

Background

Based on the average Pmmm crystal structure and the observed Q=(δ1,0,0) modulation, symmetry analysis allows several subspace groups (orthorhombic Pmmm, Pmm2, and monoclinic P2/m, Pm) for either biaxial or twinned uniaxial ordering, all involving in-plane Pr distortion modes. This structural classification is crucial to differentiating the microscopic nature of the Q1 super-lattice.

The authors explicitly state that, with their present diffraction data, they cannot distinguish between a biaxial and a twinned uniaxial configuration, highlighting the need for further experimental resolution or complementary probes to pin down the symmetry of the Q1 order.