Lecturer: Prof. Girsh Blumberg Affiliation: Department of Physics and Astronomy, Rutgers, The State University of New Jersey Abstract: Many novel electronic ground states have been found to emerge from the hybridization between localized d- or f-electron states and conduction electron states in correlated electron materials. The heavy fermion (HF) compound URu2Si2 exhibits the coexistence of two such ground states: so-called “hidden order” (HO) below THO=17.5 K and superconductivity below Tc =1.5 K. Despite 30 years of research the symmetry of the order parameter associated with HO phase below 17.5 K has remained ambiguous. Here we use polarization resolved Raman spectroscopy to specify the symmetry of the low energy excitations above and below the HO transition. These excitations involve transitions between interacting heavy uranium 5f orbitals, responsible for the broken symmetry in the HO phase. From the symmetry analysis of the collective mode, we determine that the HO parameter breaks local vertical and diagonal reflection symmetries at the uranium sites, resulting in crystal field states with distinct chiral properties, which order to a commensurate chirality density wave ground state. We explore the connection between the "hidden order" chirality density wave and the unconventional superconductivity at Tc = 1.5 K in URu2Si2, which has recently been proposed to be of a chiral d-wave type. References: Kung, H.H., Baumbach, R.E., Bauer, E.D., Thorsmolle, V.K., Zhang, W.L., Haule, K., Mydosh, J.A. and G. Blumberg. Chirality density wave of the ’hidden order’ phase in URu2Si2. Science, 347, 1339 (2015). ‏האירוע הזה כולל שיחת וידאו ב-Google Hangouts. הצטרף: https://hangouts.google.com/hangouts/_/mail.huji.ac.il/condensed?hceid=b...