Conductance anomalies in quantum wires

We study the conductance threshold of clean nearly straight quantum wires i n which an electron is bound. We show that such a system exhibits spin-depe ndent conductance structures on the rising edge to the first conductance pl ateau; one near 0.25(2e(2)/h), related to a singlet resonance, and one near 0.75(2e(2)/h), related to a triplet resonance. As a quantitative example w e solve exactly the scattering problem for two-electrons in a wire with pla nar geometry and a weak bulge. From the scattering matrix we determine cond uctance via the Landauer-Buttiker formalism. The conductance anomalies are robust and survive to temperatures of a few degrees. With increasing in-pla ne magnetic field the conductance exhibits a plateau at e(2)/ h, consistent with recent experiments.