Thermodynamic properties of Yb sub(2) Ti sub(2) O sub(7) pyrochlore as a function of temperature and magnetic field: Validation of a Quantum spin ice exchange Hamiltonian

The thermodynamic properties of the pyrochlore Yb sub(2) Ti sub(2) O sub(7) material are calculated using the numerical linked-cluster calculation method for an effective anisotropic-exchange spin-[1/2] Hamiltonian with parameters recently determined by fitting the neutron scattering spin-wave data obtained at high magnetic field. Magnetization M(T, h) as a function of temperature T and for different magnetic fields h applied along the three high-symmetry directions [100], [110], and [111] are compared with experimental measurements on the material for temperature T > 1.8 K. The excellent agreement between experimentally measured and calculated M(T, h) over the entire temperature and magnetic field ranges considered provides strong quantitative validation of the effective Hamiltonian. It also confirms that fitting the high-field neutron spin-wave spectra in the polarized paramagnetic state is an excellent method for determining the microscopic exchange constants of rare-earth insulating magnets that are described by an effective spin-[1/2] Hamiltonian. Finally, we present results which demonstrate that a recent analysis of the polarized neutron scattering intensity of Yb sub(2) Ti sub(2) O sub(7) using a random phase approximation method [Chang et al., Nat. Commun. 3. 992 (2012) (http://dx.doi.org/10.1038/ncomms1989)] does not provide a good description of M(T, h) for T [