Tomonaga-Luttinger liquid and quantum criticality in spin-½ antiferromagnetic Heisenberg chain C14H18CuN4O10 via Wilson ratio

The ground state of a one-dimensional spin-12 uniform antiferromagnetic Heisenberg chain (AfHc) is a Tomonaga–Luttinger liquid which is quantum-critical with respect to applied magnetic fields up to a saturation field μ0Hs beyond which it transforms to a fully polarized state. Wilson ratio has been predicted to be a good indicator for demarcating these phases [Phys. Rev. B 96, 220401 (2017)]. From detailed temperature and magnetic field-dependent magnetization, magnetic susceptibility and specific heat measurements in a metalorganic complex and comparisons with field theory and quantum transfer matrix method calculations, the complex was found to be a very good realization of a spin-12 AfHc. Wilson ratio obtained from experimentally obtained magnetic susceptibility and magnetic contribution of specific heat values was used to map the magnetic phase diagram of the uniform spin-12 AfHc over large regions of phase space demarcating Tomonaga–Luttinger liquid, saturation field quantum critical, and fully polarized states. Luttinger parameter and spinon velocity were found to match very well with the values predicted from conformal field theory.