title: Momentum-resolved hidden-order gap reveals symmetry breaking and origin of entropy loss in URu2Si2.
abstract: Spontaneous symmetry breaking in physical systems leads to salient phenomena at all scales, from the Higgs mechanism and the emergence of the mass of the elementary particles, to superconductivity and magnetism in solids. The hidden-order state arising below 17.5 K in URu2Si2 is a puzzling example of one of such phase transitions: its associated broken symmetry and gap structure have remained longstanding riddles. Here we directly image how, across the hidden-order transition, the electronic structure of URu2Si2 abruptly reconstructs. We observe an energy gap of 7 meV opening over 70% of a large diamond-like heavy-fermion Fermi surface, resulting in the formation of four small Fermi petals, and a change in the electronic periodicity from body-centred tetragonal to simple tetragonal. Our results explain the large entropy loss in the hidden-order phase, and the similarity between this phase and the high-pressure antiferromagnetic phase found in quantum-oscillation experiments.
authors.affiliation: 1] CSNSM, Université Paris-Sud and CNRS/IN2P3, Bâtiments 104 et 108, 91405 Orsay, France [2].
authors.forename: C
authors.initials: C
authors.lastname: Bareille
authors.affiliation: 1] Lehrstuhl für Experimentelle Physik VII, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany [2].
authors.forename: F L
authors.initials: FL
authors.lastname: Boariu
authors.affiliation: Lehrstuhl für Experimentelle Physik VII, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Schwab
authors.affiliation: 1] Univ. Grenoble Alpes, Institut Néel, F-38042 Grenoble, France [2] CNRS, Institut Néel, F-38042 Grenoble, France.
authors.forename: P
authors.initials: P
authors.lastname: Lejay
authors.affiliation: 1] Lehrstuhl für Experimentelle Physik VII, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany [2] Forschungszentrum Karlsruhe, Gemeinschaftslabor für Nanoanalytik, D-76021 Karlsruhe, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Reinert
authors.affiliation: CSNSM, Université Paris-Sud and CNRS/IN2P3, Bâtiments 104 et 108, 91405 Orsay, France.
authors.forename: A F
authors.initials: AF
authors.lastname: Santander-Syro