Atomic motions in the layered copper pseudochalcogenide CuNCN indicative of a quantum spin-liquid scenario
Andrei L Tchougréeff1,2,3, Ralf P Stoffel1, Andreas Houben1
1Institute of Inorganic Chemistry, RWTH Aachen University, D-52056 Aachen, Germany.
Abstract:
We explore the thermodynamic properties of the layered copper(II) carbodiimide CuNCN by heat-capacity measurements and investigate the corresponding thermal atomic motions by means of neutron powder diffraction as well as inelastic neutron scattering. The experiments are complemented by a combination of density-functional calculations, phonon analysis and analytic theory. The existence of a soft flexural mode-bending of the layers, characteristic for the material structure-is established in the phonon spectrum of CuNCN by giving characteristic temperature-dependent contributions to the heat capacity and atomic displacement parameters. The agreement with the neutron data allows us to extract a residual-on top of the lattice-presumably spinon contribution to the heat capacity [Formula: see text], speaking in favor of the spin-liquid picture of the electronic phases of CuNCN.
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