Two Particle Response in Cluster Dynamical Mean Field Theory Rosemary F. Wyse, Aspen Center for Physics, PHY/DMR Dynamical Mean Field Theory is a very successful theoretical description of the one electron properties of strongly correlated electrons (measured in photoemission). But wide classes of experiments including Raman and neutron scattering measure ‘two-particle’ properties. In our time at Aspen we developed a robust theoretical method for computing the two particle response in dynamical mean field theory and showed that it reproduces nontrivial features including the two magnon Raman scattering of high transition temperature superconductors. This work opens a path to systematic computation of wide classes of important experiments. Calculated B 1g symmetry Raman response of high transition temperature superconductor as a function of carrier concentration, showing two magnon peak at x=0 evolving to quasiparticle response of overdoped materials *Work done in collaboration with N. Lin and E. Gull

Nematic Order in Iron-Based-Superconductors Rosemary F. Wyse, Aspen Center for Physics, PHY/DMR During collaborations* at the Aspen Center for Physics, we demonstrated how emergent nematic order fluctuations affect both the normal and superconducting states of the iron pnictides. Nematic order, while of magnetic origin, is hard to detect yet a very powerful mechanism to enhance magnetic fluctuations, leaving distinctive signatures in the physical properties of the new iron-superconductors. This is of great importance given the strong evidence for a magnetic mechanism of superconductivity in these systems. We argue that the superconducting transition temperature, below which no electric loss occurs, is enhanced due to nematic fluctuations of magnetic origin. Our results explain numerous puzzling experiments and made predictions that could be verified in recent experimental observations. Phase diagram of a iron based superconductor with nematic order above spin-density (SDW) and superconducting (SC) phases *Work done in collab. with: E. Abrahams,, P. Chandra, A. Chubukov, R. Fernandes

Understanding the quantum mechanical rules that govern novel superconductivity is an essential step towards finding improved superconductors. The specific results here were presented in a Colloquium at the Aspen Center for Physics (ACP), aimed at all participants, across many sub-fields of physics, fostering interdisciplinary discussions and research. Outreach to the public by physicists at ACP included public lectures by Wolgang Ketterle (MIT) on ‘New Forms of Matter near Absolute Zero’ and by Chetan Nayak (UCSB) on ‘Quantum Matters’ Nematic Order in Iron-Based-Superconductors Rosemary F. Wyse, Aspen Center for Physics, PHY/DMR Unconventional superconductivity: the same electrons that generate magnetic moments and magnetism form Cooper- pairs and conduct super currents. The search for new unconventional superconductors is central to the quest for materials with better, energy efficient, electric or magnetic performance.