URu2Si2: Trying to understand the mysterious “hidden-order” phase

International audienceDuring the past 30 years the heavy fermion superconductor URu2Si2 has presented a fundamental challenge in condensed matter physics. At T0 = 17.5 K it undergoes a second-order transition from a paramagnetic to a so-called hidden-order (HO) phase, whose order parameter remains elusive despite decades of proposed theoretical models [1–4]. Previous spectroscopic work proved the existence of an electronic instability, producing a Fermi-surface reconstruction and gap opening, across the transition [5-8]. Here we provide new insight into the origin of the HO phase by a direct experimental comparison of its electronic structure with a neighboring low-temperature phase that exhibits well-defined antiferromagnetic (AFM) order, obtained by means of an effective chemical pressure through the partial substitution of Ru with Fe [9]. Our study underlines the key role of hybridization between the heavy fermion and the conduction band states in driving the HO transition, and reveals variations in this interaction across the HO-AFM phase boundary.[1] J. A. Mydosh and P. M. Oppeneer, Rev. Mod. Phys 83, 1301 (2011).[2] P. Chandra, P. Coleman, J. A. Mydosh, and V. Tripathi, Nature 417, 831 (2002).[3] M. B. Maple, J. W. Chen, Y. Dalichaouch, T. Kohara, C. Rossel and M. S. Torikachvilli, Phys. Rev. Lett. 56, 185 (1986).[4] J. A. Mydosh and P. M. Oppeneer, Philos. Mag. 94, 3642 (2014).[5] A. F. Santnder-Syro, M. Klein, F. L. Boariu, A. Nuber, P. Lejay and F. Reinert, Nat. Phys. 5, 637 (2009).[6] A. R. Schmidt, M. H. Hamidian, P. Wahl, F. Meier, A. V. Balatsky, J. D. Garrett, T. J. Williams, G. M. Luke and J. C. Davis, Science 465, 570 (2010).[7] S. Chatterjee, J. Trinckauf, T. Hänke, D. E. Shai, J. W. Harter, T. J. Williams, G. M. Luke, K. M. Shen and J. Geck, Phys. Rev. Lett. 110, 186401 (2013).[8] C. Bareille, F. L. Boariu, H. Schwab, P. Lejay, F. Reinert and A. F. Santander-Syro, Nat. Commun. 5, 4326 (2014).[9] E. Frantzeskakis, J. Dai, T. C. Rödel, M. Güttler, C. Bareille, M. Thees, E. D. L. Rienks, F. Fortuna, M. B. Maple and A. F. Santander-Syro (submitted, 2019)