Study of spin transport in In0.75Ga0.25As/In0.75Al0.25As narrow wires

We systematically studied spin–orbit interaction in narrow wires with different wire widths, where the base material is a normal-type In0.75Ga0.25As/In0.75Al0.25As modulation-doped narrow-gap heterojunction. We used two different methods to make the wires and analyze their spin-dependent transports. As a first method, the wire width was defined by simply mesa-etching the samples on the same substrate. As a second method, we fabricated wire samples with side-gate. The wire width was changed by varying a voltage applied to the side-gate. For the determination of spin–orbit coupling constant, <f>α,</f> we measured magneto-resistance at 1.6 K. In the first method, <f>α</f> remained almost constant in the wires with various widths longer than 0.4 μm. However, in the second method, <f>α</f> increased with decreasing the wire width down to about 1 μm. The increase of <f>α</f> observed in the side-gate structure sample might rather be attributed to the effect of the lateral electric field by the side-gate, which could enhance the effect of the vertical electric field originally existing at the hetero-interface. [Copyright &y& Elsevier]