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2.00 pm, Lecture Hall 4 Non-perturbative and perturbative non-Fermi Liquids Shouvik Sur McMaster U. 25-09-14 Abstract At the quantum critical point (QCP) that separates a conventional metallic phase (described by Fermi liquid theory) from a symmetry broken phase such as a magnet, the quasiparticles in the metal decohere due to scatterings with critical fluctuations of the order parameter. The eventual fate of the metal in such a situation 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 comprehension of their respective ground states. In this talk I will present two cases where it is possible to have a controlled access to the low energy physics at such metallic critical points. In the first case, we study the critical theory that governs the QCP for the quantum phase transition from a chiral metal to an exciton condensate state. Strong kinematic constraints, imposed by the chirality of fermion dynamics, leads to the determination of exact critical exponents at the infra-red fixed point. This proffers a first example of a non-Fermi liquid state in two space-dimensions realized within physical parametric regime. In the second 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 three and below. Herein we uncover a novel non-Fermi liquid state which is stabilized by a subtle balance between screening of interactions and emergent dimensional reduction.
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