Neutron scattering evidence for isolated spin-1/2 ladders in (C${}_5$D${}_{12}$N)${}_2$CuBr${}_4$

Abstract

Inelastic neutron scattering was used to determine the spin Hamiltonian for the singlet ground state system of fully deuterated BPCB, (C${}_5$D${}_{12}$N)${}_2$CuBr${}_4$. A 2-leg spin-1/2 ladder model, with $J_{\perp }=(1.09\pm 0.01)$ meV and $J_{\Vert }=(0.296\pm 0.005)$ meV, accurately describes the data. The experimental limit on the effective inter-ladder exchange constant is $|J_{\mathrm{int}}^{\mathrm{eff}}|\lesssim 0.006$ meV, and the limit on total diagonal, intra-ladder exchange is $|J_F+J_{F^{\prime }}|\le 0.1$ meV. Including the effects of copper to bromide covalent spin transfer on the magnetic form-factor, the experimental ratios of intra-ladder bond energies are consistent with the predictions of continuous unitary transformation.

10 pages, with 11 figures