Dimensional Evolution of Spin Correlations in the Magnetic Pyrochlore   Yb2Ti2O7
  The pyrochlore material Yb2Ti2O7 displays unexpected quasi-two-dimensional (2D) magnetic correlations within a cubic lattice environment at low temperatures, before entering an exotic disordered ground state below T=265mK. We report neutron scattering measurements of the thermal evolution of the 2D spin correlations in space and time. Short range three dimensional (3D) spin correlations develop below 400 mK, accompanied by a suppression in the quasi-elastic (QE) scattering below ~ 0.2 meV. These show a slowly fluctuating ground state with spins correlated over short distances within a kagome-triangular-kagome (KTK) stack along [111], which evolves to isolated kagome spin-stars at higher temperatures. Furthermore, low-temperature specific heat results indicate a sample dependence to the putative transition temperature that is bounded by 265mK, which we discuss in the context of recent mean field theoretical analysis. 
K. A. Ross, L. R. Yaraskavitch, M. Laver, J. S. Gardner, J. A.   Quilliam, S. Meng, J. B. Kycia, D. K. Singh, H. A. Dabkowsk...
cond-mat.str-el