Quantum point contacts are narrow constrictions in a two-dimensional electron system formed by electrostatic gating. Owing to the lateral confinement, the conductance through the point contact is quantized in integer multiples of 2e2/h, where e is the fundamental charge and h is the Planck constant. An anomaly appears at 0.7 × 2e2/h, the origin of which has been tentatively explained by competing theories that predict distinct spin arrangements. Now, Minoru Kawamura and colleagues at the RIKEN Center for Emergent Matter Science, Slovak Academy of Sciences and Ibaraki University have measured the electronic magnetization in the point contact, providing insight into the origin of the 0.7 feature.
The researchers measured the conductance of a point contact fabricated from GaAs/AlGaAs high-mobility heterostructures in the presence of an in-plane magnetic field, at a temperature of 20 mK. They demonstrated resistive detection of nuclear magnetic resonance, from which the electron magnetization can be inferred. This is a new technique of measuring the magnetization of a few electron spins. The team found that the magnetization changes smoothly as the gate voltage is increased; these results are consistent with a model in which there are no bound states in the point contact that could give rise to the 0.7 anomaly, ruling out theories that are inconsistent with this picture.
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De Ranieri, E. Quantum point contacts: Measuring spins. Nature Nanotech (2015). https://doi.org/10.1038/nnano.2015.211
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DOI: https://doi.org/10.1038/nnano.2015.211
