The 0.7 anomaly in one-dimensional hole quantum wires

In this paper we study the anomalous 0.7 structure in high quality ballistic one-dimensional hole systems. Hole systems are of interest because of their large effective mass, strong spin?orbit coupling, as well as having spin?3/2 compared to spin?1/2 for electrons. We observe remarkably clean conductance quantization in a variety of different samples, and a strong feature at ~0.7 ? 2e2/h, which shows a similar temperature and density dependence to the 0.7 feature observed in electron systems. In contrast to the case for electrons, the strong spin?orbit coupling results in an anisotropic Zeeman splitting, which we use to probe the 0.7 feature and the associated zero-bias anomaly. Our results indicate that the 0.7 feature and the zero-bias anomaly are related, and both are suppressed by spin polarization. These results place valuable constraints on models of the microscopic origins of the 0.7 feature.