To establish the microscopic model of the compound ${\mathrm{BiCu}}_2{\mathrm{PO}}_6$ is a challenging task. Inelastic neutron scattering experiments showed that the dispersion of this material is nondegenerate suggesting the existence of anisotropic interactions. Here we present a quantitative description of the excitation spectrum for ${\mathrm{BiCu}}_2{\mathrm{PO}}_6$ on the one-particle level. The solution of the isotropic frustrated spin ladder by continuous unitary transformations is the starting point of our approach. Further couplings such as isotropic interladder couplings and anisotropic interactions are included on the mean-field level. Our aim is to establish a minimal model built on the symmetry-allowed interactions and to find a set of parameters which allows us to describe the low-energy part of the dispersion without assuming unrealistic couplings.

• Received 13 July 2016

DOI:https://doi.org/10.1103/PhysRevB.94.155115