Anomalous scaling of conductivity in integrable fermion systems

Department of Physics, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom(Dated: 2nd February 2008)We analyze the high-temperature conductivity in one-dimensional integrable models of interacting fermions:the t-V model (anisotropic Heisenberg spin chain) and the Hubbard model, at half-filling in the regime cor-responding to insulating ground state. A microcanonical Lanczos method study for finite size systems revealsanomalously large finite-size effects at low frequencies while a frequency-moment analysis indicates a finited.c. conductivity. This phenomenon also appears in a prototype integrable quantum system of impenetrableparticles, representing a strong-coupling limit of both models. In the thermodynamic limit, the two results couldconverge to a finite d.c. conductivity rather than an ideal co nductor or insulator scenario.