Statistical theory of transport by strongly interacting lattice fermions

We present a study of electric transport at high temperature in a model of strongly interacting spinless fermions without disorder. We use exact diagonalization to study the statistics of the energy eigenvalues, eigenstates, and the matrix elements of the current. These suggest that our nonrandom Hamiltonian behaves like a member of a certain ensemble of Gaussian random matrices. We calculate the conductivity sigma(omega) and examine its behavior, both in finite-size samples and as extrapolated to the thermodynamic limit. We find that sigma(omega) has a prominent nondivergent singularity at omega=0 reflecting a power-law long-time tail in the current autocorrelation function that arises from nonlinear couplings between the long-wavelength diffusive modes of the energy and particle number.