Mon, Oct 3, 2016, 1:15 pm to 2:30 pm
PCTS Seminar Room
Models for metallic anti-ferromagnets map to the dissipative XY model as do XY ferromagnets, the superconductor-insulator transition, and the model forloop-current order in Cuprates. The spectral function of the quantum-critical fuctuations for this model in 2D for a range of parameters is determined by topological defects - instantons and 2D vortices; it is a separable function of space and time, with a 1= dependence at criticality. The marginal fermi-liquid properties for the fermions follow from coupling to such fluctuations. These fluctuations are directly measured by inelastic neutron scattering in the quantum-critical region of the new Fe- based compounds, in a 2D ferromagnet and in heavy-Fermions, and deduced in cuprates through analysis of ARPES. ARPES also reveals the coupling function of the fermions to the fluctuations so as to give nearly angle-independent normal self-energy but d-wave pairing energy.