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Hofman, Diego

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Hofman, Diego

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Author's Publications: search.filters.isAuthorOfPublication.4bbbcfec-c733-414d-887b-a545f0014563

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    Quantum Critical Response at the Onset of Spin Density Wave Order in Two-dimensional Metals
    (American Physical Society, 2011) Hartnoll, Sean; Hofman, Diego; Metlitski, Max; Sachdev, Subir
    We study the frequency dependence of the electron self-energy and the optical conductivity in a recently developed field theory of the spin-density-wave quantum phase transition in two-dimensional metals. We focus on the interplay between the Fermi surface “hot spots” and the remainder of the “cold” Fermi surface. Scattering of electrons off the fluctuations of the spin-density-wave order parameter, \(\varphi\), is strongest at the hot spots; we compute the conductivity due to this scattering in a rainbow approximation. We point out the importance of composite operators, built of products of the primary electron or \(\varphi\) fields: These have important effects also away from the hot spots. The simplest composite operator, \(\varphi^2\), leads to deviations from Landau Fermi-liquid behavior on the entire Fermi surface. We also find an intermediate frequency window in which the cold electrons lose their quasiparticle form due to effectively one-dimensional scattering processes. The latter processes are part of umklapp scattering, which leads to singular contributions to the optical conductivity at the lowest frequencies at zero temperature.
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    Chiral Scale and Conformal Invariance in 2D Quantum Field Theory
    (American Physical Society, 2011) Hofman, Diego; Strominger, Andrew
    It is well known that a local, unitary Poincaré-invariant 2D quantum field theory with a global scaling symmetry and a discrete non-negative spectrum of scaling dimensions necessarily has both a left and a right local conformal symmetry. In this Letter, we consider a chiral situation beginning with only a left global scaling symmetry and do not assume Lorentz invariance. We find that a left conformal symmetry is still implied, while right translations are enhanced either to a right conformal symmetry or a left U(1) Kac-Moody symmetry.