## Quantum Critical Fluctuations Leading to Strange Metals in 2D Metallic Anti-ferromagnets, Ferromagnets and in the Cuprates

**Speaker:**Chandra Varma, University of California - Riverside

**When:**October 23, 2015 (Fri), 12:00PM to 01:30PM (add to my calendar)

**Location:**SCI 352

*This event is part of the Biophysics/Condensed Matter Seminar Series. *

Models for metallic anti-ferromagnets map to the dissipative XY model as do XY ferromagnets, the superconductor-insulator transition, and the model for loop-current order in Cuprates. The spectral function of the quantum-critical

uctuations 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 uctuations. These uctuations 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 uctuations so as to give nearly angle-independent normal self-energy but d-wave pairing energy.