Spin-polarized transport in adiabatic quantum point contact with strong Rashba spin-orbit interaction

We first report 0.5(2e2/h) conductance quantization in adiabatic quantum point contacts (QPCs) fabricated at high In-content InGaAs/InAlAs single heterojunctions under no magnetic field. This quantization seems difficult to understand, since the spin one-dimensional (1D) subbands in the QPCs are generally degenerated when B=0. However, this observation is reproducible in various QPC samples with different dimensions but not likely so definite as the conductance quantization in usual QPCs. It is noted that this particular heterojunction 2DEG is found to have high electron mobility of <5×105 cm2/Vs as well as very large Rashba spin-orbit (SO) coupling constant of <35×10−12 eVm. So that, the QPCs realized here can be regarded as a kind of Tomonaga-Luttinger wire with an enhanced Rashba interaction. In such a case, a mode coupling between the Rashba splitting 1D subbands gives rise to a spin-polarized transport in each ±k direction. This theory could be the one plausible candidate to explain the 0.5(2e2/h) conductance quantization observed here in the adiabatic QPC. This finding would be developed to novel spin-filters or spin-directional coupler devices based on nonmagnetic semiconductors.