Anomalous Conductance Quantization in Side-Gated InAs Quantum Point Contacts*

Conductance measurements as function of Fermi energy of InAs quantum point contacts created by side gating on InAs/InAlAs quantum-well structure exhibit a distinct plateau at e$^{2}$/h and a less distinct one at 2e$^{2}$/h. Applied magnetic field has little or no influence on the conductance quantization pattern. We believe the conductance plateau at e$^{2}$/h indicates a spin contribution of h/e$^{2}$ to the resistance of the one-dimensional channel when the electron density is low and the electron-electron interaction is strong. This can be understood in the framework of the recently proposed spin-incoherent Luttinger liquid (SILL) state that is considered to exist when \textit{J$<<$T$<<$E}$_{F}$, where $J$ is the spin exchange constant and E$_{F}$ the Fermi energy. In the SILL regime, the spin excitations are reflected back to the leads reducing the conductance of the quantum wire to e$^{2}$/h. At higher Fermi energy, when the electron density is higher, the spin contribution to resistance vanishes and the conductance takes the well-known quantized value of 2e$^{2}$/h.