Towards a microscopic theory of the 0.7 anomaly

A microscopic mechanism for the so-called 0.7 anomaly is proposed. The exchange interactions in a constriction develop electron spin fluctuations with decreasing carrier density. For non-adiabatic transmission, this spin fluctuation causes additional electron backscattering. The position of the anomaly and its shape are explained by the energy dependence of the transmission probability through the static potential. The temperature dependence is also given by our model.