Strong and Tunable Spin-Orbit Coupling of One-Dimensional Holes in Ge/Si Core/Shell Nanowires

We investigate the low-temperature magneto-transport properties of individual Ge/Si core/shell nanowires. Negative magneto-conductance was observed, which is a signature of one-dimensional weak antilocalization of holes in the presence of strong spin-orbit coupling. The temperature and back gate dependences of phase coherence length, spin-orbit relaxation time, and background conductance were studied. Specifically, we show that the spin orbit coupling strength can be modulated by more than five folds with an external electric held. These results suggest the Ge/Si nanowire system possesses strong and tunable spin-orbit interactions and may serve as a candidate for spintronics applications.