title: Dynamical Response near Quantum Critical Points.
abstract: We study high-frequency response functions, notably the optical conductivity, in the vicinity of quantum critical points (QCPs) by allowing for both detuning from the critical coupling and finite temperature. We consider general dimensions and dynamical exponents. This leads to a unified understanding of sum rules. In systems with emergent Lorentz invariance, powerful methods from quantum field theory allow us to fix the high-frequency response in terms of universal coefficients. We test our predictions analytically in the large-N O(N) model and using the gauge-gravity duality and numerically via quantum Monte Carlo simulations on a lattice model hosting the interacting superfluid-insulator QCP. In superfluid phases, interacting Goldstone bosons qualitatively change the high-frequency optical conductivity and the corresponding sum rule.
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.|Department of Physics, Stanford University, Stanford, California 94305, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Lucas
authors.affiliation: Department of Physics, University of California, Berkeley, Berkeley, California 94720, USA.
authors.forename: Snir
authors.initials: S
authors.lastname: Gazit
authors.affiliation: Physics Department, Technion, 32000 Haifa, Israel.
authors.forename: Daniel
authors.initials: D
authors.lastname: Podolsky
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.|Département de Physique, Université de Montréal, Montréal (Québec), H3C 3J7, Canada.
authors.forename: William
authors.initials: W
authors.lastname: Witczak-Krempa