ARPES Clues to the Hidden Order in URu$_{2}$Si$_{2}$*

The three-dimensional electronic structure of UHV-cleaved URu$_{2}$Si$_{2}$ is investigated using photon-dependent angle-resolved photoemission (ARPES). Wide angle Fermi-surface (FS) maps as well as high-resolution spectroscopy focused on key high symmetry points reveal high U 5$f$ spectral weight at the hole-like regions of the $\Gamma $ and Z-points. The small hole-surface FS topologies have good size correspondence to dHvA FS orbit frequencies, but do not agree well with LDA band structure calculations. More favorable correspondence of the URu$_{2}$Si$_{2}$ ARPES is made to LDA+DMFT calculations as well as to detailed ARPES measurements of 5$f^{0}$ ThRu$_{2}$Si$_{2}$. Special attention was given to spatial-dependent characterization of the cleave surface in order to understand the possible cleave terminations and to avoid surface effects related to disorder or non-bulk coordinated U-termination. Theoretical surface slab calculations assist in identifying surface-termination related features at the X-point. In addition, we propose a model for the incommensurate nesting vectors, 0.6a* and 1.4a*, observed by inelastic neutron scattering\footnote{C. Wiebe \textit{et al}., Nat Phys. \textbf{3}, 96 (2007)} to be characteristic of the hidden order phase of URu$_{2}$Si$_{2}$. Finally, preliminary ARPES results for URu$_{2-x}$Re$_{x}$Si$_{2}$ give a clue as to the mechanism by which Re doping suppresses the hidden order phase in favor of ferromagnetism.