Spin effects in one-dimensional systems

We review the progress in the study of the 0.7 structure, a many-body spin effect observed in GaAs quantum wires. Electrical and thermal measurements show that the 0.7 structure is characterized by a spontaneous spin splitting which causes the spin-up subband to stay near the electrochemical potential as the channel is populated. The 0.7 structure is not an isolated phenomenon but is the first in a series of effects that occur whenever opposite spin subbands are degenerate in energy. Bias spectroscopy shows how the levels move with increasing source–drain bias as the 0.7 structure evolves into a structure near 0.85(2e²/h). Our measurements do not support a Kondo effect from a single bound state in the channel as a possible explanation of the 0.7 structure.