R. G. Herb Condensed Matter Seminars
We measure the anisotropy of spin-orbit interaction (SOI) using real-time charge detection of single electrons tunneling between different states of GaAs/AlGaAs-based double quantum dots (DQDs). The strength of the SOI depends on the crystallographic direction of the electron tunneling, and on the relative alignment between the tunneling direction and the spin quantization axis. In the DQD, the tunneling direction is defined by the main axis of the device, and the spin quantization axis is chosen by the direction of an external in-plane magnetic field. This set-up allows us to control the strength of the spin-orbit interaction and leads to spin lifetimes of 10 s.
We fabricate two DQDs on a GaAs heterostructure, one with its main axis along the  crystal axis, and another one with the main axis rotated by 90 degrees, i.e. along [-110]. By applying suitable gate voltages to metallic top-gates, each DQD is brought into a configuration where two electrons reside in the device, and tunneling to the source and drain is suppressed. Using a charge detector, we distinguish between two resonant charge states: one state where both electrons reside in the right quantum dot, (0,2), and one state where each dot is occupied by a single electron, (1,1). We argue that in this configuration, the Pauli spin blockade can be used to measure the strength of the spin--orbit interaction experienced by tunneling electrons.
We use the two DQDs for measuring the different strengths of the SOI experienced by electrons moving along distinct crystallographic axes. We find that the SOI induces spin-flips for electrons moving along , and that the SOI vanishes for an electron moving along [-110]. For a given tunneling direction, we vary the strength of the experienced SOI by changing the alignment between the tunneling direction and spin-quantization axis by means of rotating the direction of the applied in-plane field. We find a sinusoidal dependence on the relative angle between the two directions.
A high magnetic field facilitates suppression of incoherent spin-relaxation processes within single dots. We measure the anisotropy of spin-flip tunneling rates between two energetically resonant quantum states in this setting and find that the spin--orbit interaction can be turned from on to almost completely off.