The 0.7 anomaly in quantum point contact; many-body or single-electron   effect?
  Apart from usual quantization steps on the ballistic conductance of a quasi-one-dimensional conductor, an additional plateau-like feature appears at a fraction of about 0.7 below the first conductance step in GaAs-based quantum point contacts (QPCs). Despite a tremendous amount of research on this anomalous feature, its origin remains still unclear. Here, a unique model of this anomaly is proposed relied on fundamental principles of quantum mechanics. It is noticed that just after opening a quasi-1D conducting channel in the QPC a single electron travels the channel at a time, and such electron can be - in principle - observed. The act of observation destroys superposition of spin states, in which the electron otherwise exists, and this suppresses their quantum interference. It is shown that the QPC-conductance is then reduded by a factor of 0.74. "Visibility" of electron is enhanced if the electron spends some time in the channel due to resonant transmission. Electron's resonance can also explain an unusual temperature behaviour of the anomaly, as well as its recently discovered feature: oscillatory modulation as a function of the channel length and electrostatic potential. A recipe for experimental verification of the model is given. 
Tadeusz Figielski
cond-mat.mes-hall