Global k-space perspective and Temperature Dependence of f-states in URu2Si2

Jonathan Denlinger (Advanced Light Source, Lawrence Berkeley National Laboratory)

The heavy fermion compound URu2Si2 possesses a transition below 17.5K into a Hidden Order phase of whose unknown order parameter has been intensely researched for almost 40 years. Recent high-resolution angle-resolved photoemission (ARPES) measurements from four different groups have identified a narrow band of f-states close to the Fermi level in a narrow k-space range around the surface zone center revealing varying ways in which energy shifts, back-folding of states and/or spectral weight sharpening possibly correlate to the hidden order transition at 17.5K. We attempt to provide a more global k-space context for the presence of such f-states and their relation to the bulk Fermi surface topology using synchrotron-based wide-angle and photon energy-dependent ARPES mapping of the electronic structure in multiple Brillouin zones. In addition, x-ray polarization and small-spot spatial dependences are exploited to assist identification of narrow-band f-states and their relation to specific U- or Si-terminations of the cleaved surface. The bulk FS topology is critically compared to LDA theory and is shown to be distinctly different from both the localized ThRu2Si2-like f-core calculation and the fully f-itinerant calculation. Finally we are able to identify particular k-space regions away from the high-symmetry zone center that match a 0.6a* incommensurate wave vector kF separation that exhibit dramatic electronic structure changes that are abrupt at the hidden order transition and whose evolution to higher temperatures correlates to a gradual Kondo coherence transition below ~50K.

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