Neutron scattering evidence for isolated spin-1/2 ladders in (C5D12N)2CuBr4

Inelastic neutron scattering was used to determine the spin Hamiltonian for the singlet ground state system (C5D12N)2CuBr4 (BPCB). A 2-leg spin 1/2 ladder model, with J? = 1:084 0:005 meV and Jk = 0:321 0:008 meV, accurately describes the data. The experimental limit on the inter-ladder exchange constant is jJ0j 0.005 meV, and the limit on diagonal, intra-ladder exchange is jJF j 0.1 meV. The experimental ratios of intra-ladder bond energies are consistent with the predictions of continuous unitary transformations calculations.