Special CPM Seminar

Perturbative and exact non-Fermi Liquids.

Shouvik Sur

McMaster University

At a quantum critical point (QCP) associated with a symmetry breaking phase transition in a metal, the quasiparticles decohere due to scatterings with critical fluctuations of the order parameter. The eventual fate of the metal in the low energy limit is of great interest due to the possibility of formation of non-Fermi liquid states. Generally, in two space dimensions, theories that describe the QCP become strongly interacting at low energies, which prevents a systematic understanding of their low temperature behaviours. In this talk I will present two cases, where it is possible to have a controlled access to the low energy physics at metallic critical points. In the first case, we explore the antiferromagnetic QCP that is relevant to systems like cuprate superconductors, heavy fermion compounds and iron-based superconductors. We achieve control over the strong quantum fluctuations by embedding the one-dimensional Fermi surface in space-dimensions greater than two. Herein we uncover a novel non-Fermi liquid state which is stabilized by a subtle balance between screening of interactions and emergent dimensional reduction. In the second case, we study the critical theory that governs the quantum phase transition from a chiral metal to an exciton condensate. Strong kinematic constraints, imposed by the chirality of electron dynamics, leads to the determination of exact critical exponents at the infrared fixed point. This offers a first example of a non-Fermi liquid state in two space-dimensions, where exact scaling properties are computable.