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

TL;DR

This study uses neutron scattering to precisely characterize the spin interactions in a deuterated ladder compound, confirming a 2-leg spin-1/2 ladder model with minimal inter-ladder coupling.

Contribution

The paper provides detailed experimental determination of the spin Hamiltonian parameters for (C$_5$D$_{12}$N)$_2$CuBr$_4$, establishing it as an isolated spin-1/2 ladder system with quantified exchange interactions.

Findings

Accurate values for intra-ladder exchange constants: J_perp and J_parallel.

Experimental upper limit on inter-ladder coupling: |J_int^{eff}| ≤ 0.006 meV.

Consistency of bond energy ratios with continuous unitary transformation predictions.

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 $J_\bot = (1.09 \pm 0.01)$ meV and $J_\| = (0.296 \pm 0.005)$ meV, accurately describes the data. The experimental limit on the effective inter-ladder exchange constant is $|J_{\rm int}^{\rm eff}|\lesssim 0.006$ meV, and the limit on total diagonal, intra-ladder exchange is $|J_F+J_{F'}|\leq 0.1$ 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.