Spinon Excitations in 99.9% Deuterated Single Crystals of Tomonaga–Luttinger Liquid [Cu(μ‑C2O4)(4-Aminopyridine)2(H2O)]n

In this work, we describe the spinon spectrum obtained in deuterated single crystals of the spin 1/2 Heisenberg antiferromagnet [Cu(μ-C2O4)(4-aminopyridine)2(H2O)]n whose ground state is a Tomonaga–Luttinger liquid (TLL). High-resolution mass spectroscopy indicated at least 99.9% deuteration achieved in [Cu(μ-C2O4)(4-aminopyridine)2(H2O)]n that resulted in minimal background noise arising due to an incoherent scattering cross-section of residual H atoms in inelastic neutron-scattering measurements. The deuteration of starting reagents was performed by employing the method of H/D exchange using D2O as a solvent and Pd/C as a catalyst. From single-crystal X-ray diffraction (SCXRD) measurements, the crystal structure was found to be monoclinic with a C2 space group, unchanged from its undeuterated version. Calculated bond lengths and bond angles from density functional theory using dual basis were found to match very well with those obtained from ScXRD data. The 3500 cm–1 Infrared and Raman frequencies of the undeuterated crystals were found to be shifted in the lower range of 2000–3000 cm–1 in the deuterated crystals due to the C–H bonds of 4-aminopyridine. Magnetization measurements yielded the ground state of deuterated [Cu(μ-C2O4)(4-aminopyridine)2(H2O)]n to be that of a spin 1/2 antiferromagnetic Heisenberg chain TLL, which was confirmed by the observation of a spinon spectrum that are characteristic excitations of the TLL state.