Direction-resolved transport and possible many-body effects in one-dimensional thermopower

A single-particle theory due to Mott predicts a proportionality between the diffusion thermopower and the energy derivative of the logarithm of the conductance. Measurements of a ballistic 1D wire show that the Mott theory remains valid in the presence of a finite current, and that it leads to a direction-sensitive probe of electron transport. We observe an apparent violation of the Mott model at low electron densities, when there is a nonquantized plateau in the conductance at ${0.7(2e}^2/h).\mathrm{}$ There is as yet no successful theoretical explanation of this so called 0.7 structure, but the distinctive thermopower signature, which deviates from single-particle predictions, may provide the key to a better understanding.