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Phys Rev Lett ; 108(24): 241601, 2012 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-23004258


Efficient momentum relaxation through umklapp scattering, leading to a power law in temperature dc resistivity, requires a significant low energy spectral weight at finite momentum. One way to achieve this is via a Fermi surface structure, leading to the well-known relaxation rate Γ∼T2. We observe that local criticality, in which energies scale but momenta do not, provides a distinct route to efficient umklapp scattering. We show that umklapp scattering by an ionic lattice in a locally critical theory leads to Γ∼T(2Δ(k(L))). Here Δ(k(L))≥0 is the dimension of the (irrelevant or marginal) charge density operator J(t)(ω,k(L)) in the locally critical theory, at the lattice momentum k(L). We illustrate this result with an explicit computation in locally critical theories described holographically via Einstein-Maxwell theory in Anti-de Sitter spacetime. We furthermore show that scattering by random impurities in these locally critical theories gives a universal Γ∼(log(1/T))(-1).

Phys Rev Lett ; 107(16): 161601, 2011 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-22107375


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.