| The surface of a solid may exhibit electronic phases that break a symmetry present in the material's bulk. High-resolution ARPES can probe them with unique sensitivity and selectivity. I will briefly discuss two such examples, where peculiar surface electronic structures result from qualitatively different mechanisms. In the layered compound 1T-TaSe2 enhanced electronic correlations lead to a Mott insulator phase on top of a metallic bulk. In the epitaxial BiAg2 surface alloy, the breaking of inversion symmetry in the presence of spin-orbit interaction lifts the Kramers' spin degeneracy, and states of opposite spin are separated with a giant momentum splitting (δk = 0.13 Å). |
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