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 spin3/2 compared to spin1/2 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.