We study an electron interferometer formed with a quantum point contact and a scanning probe tip in a two-dimensional electron gas. The images giving the conductance as a function of the tip position exhibit fringes spaced by half the Fermi wavelength. For a contact opened at the edges of a quantized conductance plateau, the fringes are enhanced as the temperature T increases and can persist beyond the thermal length l(T). This unusual effect is explained by assuming a simplified model: The fringes are mainly given by a contribution which vanishes when T→0 and has a decay characterized by a T-independent scale.

We study chaotic scattering outside the wide band limit, as the Fermi energy EF approaches the band edges EB of a one-dimensional lattice embedding a scattering region of M sites. We show that the delay-time and thermopower distributions differ near the edges from the universal expressions valid in the bulk. To obtain the asymptotic universal forms of these edge distributions, one must keep constant the energy distance EF − EB measured in units of the same energy scale proportional to ∝ M −1/3 which is used for rescaling the energy level spacings at the spectrum edges of large Gaussian matrices. In particular the delay-time and the thermopower have the same universal edge distributions for arbitrary M as those for an M = 2 scatterer, which we obtain analytically.