Bounded diffusion

Wolfgang Paul, Jörg Baschnagel

Marko Medenjak, Christoph Karrasch, Tomaž Prosen

We establish a general connection between ballistic and diffusive transport in systems where the ballistic contribution in the canonical ensemble vanishes. A lower bound on the Green-Kubo diffusion constant is derived in terms of the curvature of the ideal transport coefficient, the Drude weight, with respect to the filling parameter. As an application, we explicitly determine the lower bound on the high-temperature diffusion constant in the anisotropic spin-1/2 Heisenberg chain for anisotropy parameters Δ≥1, thus, settling the question of whether or not the transport is subdiffusive. Additionally, the lower bound is shown to saturate the diffusion constant for a certain classical integrable model.

Eric A. Carlen

Ali Reza Mokhtari, Seyed Ali Hosseini Mansoori, Kazem Bitaghsir Fadafan

In this paper, we investigate the behavior of the thermoelectric DC conductivities in the presence of Weyl corrections with momentum dissipation in the incoherent limit. Moreover, we compute the butterfly velocity and study the charge and energy diffusion with broken translational symmetry. Our results show that the Weyl coupling γ, violates the bounds on the charge and energy diffusivity. It is also shown that the Weyl corrections violate the bound on the DC electrical conductivity in the incoherent limit.

Sushanta Dattagupta, Sanjay Puri

Thomas Hartman, Sean A. Hartnoll, Raghu Mahajan

The linear growth of operators in local quantum systems leads to an effective light cone even if the system is nonrelativistic. We show that the consistency of diffusive transport with this light cone places an upper bound on the diffusivity: D≲v^{2}τ_{eq}. The operator growth velocity v defines the light cone, and τ_{eq} is the local equilibration time scale, beyond which the dynamics of conserved densities is diffusive. We verify that the bound is obeyed in various weakly and strongly interacting theories. In holographic models, this bound establishes a relation between the hydrodynamic and leading nonhydrodynamic quasinormal modes of planar black holes. Our bound relates transport data-including the electrical resistivity and the shear viscosity-to the local equilibration time, even in the absence of a quasiparticle description. In this way, the bound sheds light on the observed T-linear resistivity of many unconventional metals, the shear viscosity of the quark-gluon plasma, and the spin transport of unitary fermions.