Speaker: Max Metlitski, Kavli Institute for Theoretical Physics, UC-Santa Barbara
Abstract: States of matter with a sharp Fermi-surface but no well-defined Landau quasiparticles are expected to arise in a number of physical systems. Examples include i) the spinon Fermi-surface (U(1) spin-liquid) state of a Mott insulator, ii) the Halperin-Lee-Read composite fermion liquid state of a half-filled Landau level and iii) quantum critical points associated with the onset of order in metals. In this work, we use renormalization group techniques to investigate possible instabilities of such non-Fermi-liquids to pairing. We show that for a large class of phase transitions in metals, the attractive interaction mediated by order parameter fluctuations always leads to a superconducting instability, which preempts the non-Fermi-liquid effects. On the other hand, the spinon Fermi-surface and the Halperin-Lee-Read states are stable against pairing for a sufficiently weak attractive short-range interaction. However, once the strength of attraction exceeds a critical value, pairing sets in. We describe the ensuing quantum phase transition between i) the U(1) and the Z2 spin-liquid states, and ii) the Halperin-Lee-Read and Moore-Read states.