Transport through a finite Hubbard chain connected to reservoirs

The dc conductance gN through a finite Hubbard chain of size N (=1,2,3,) connected to reservoirs is studied at $T=0$ in an electron-hole symmetric case. We calculate a spatial dependence of the self-energy analytically at ω=0 within the second order in U, and obtain an inter-site Green's function GN1, from which gN can be determined, via the Dyson equation. The results depend strongly on whether N is even or odd. For odd N, a perfect transmission occurs, and gN≡2e²/h independent of the values of U. This may be attributed to a Kondo resonance appearing at ω=0. For even N, gN decreases with increasing N, and converges to a finite constant which is a smooth decreasing function of U. These behaviors are essentially owing to the presence of the reservoirs, which makes a quasiparticle description valid for low-energy states at ωvF/(Na); where vF is the Fermi velocity and a is the lattice constant.