  The conditions for a spontaneous spin polarization in a quantum wire
positioned in a zero magnetic field are analyzed under weak population of
one-dimensional subbands that gives rise to the efficient quenching of the
kinetic energy by the exchange energy of carriers. The critical linear
concentration of carriers above which the quasi one-dimensional gas undergoes a
complete spin depolarization is determined by the Hartree-Fock approximation.
The dependence of the critical linear concentration on the concentration of
carriers is defined to reveal the interplay of the spin depolarization with the
evolution of the 0.7 (2e2/h) feature in the quantum conductance staircase from
the e2/h to 3/2 (e2/h) values. This dependence is used to study the effect of
the hole concentration on the 0.7 (2e2/h) feature in the quantum conductance
staircase of the quantum wire prepared inside the p-type silicon quantum well
using the split-gate technique. The 1D channel is demonstrated to be
spin-polarized at the linear concentration of holes lower than the critical
linear concentration, because the 0.7 (2e2/h) feature is close to the value of
0.5 (2e2/h) that indicates the spin degeneracy lifting for the first step of
the quantum conductance staircase. The 0.7 (2e2/h) feature is found to take
however its normal magnitude when the linear concentration of holes attains the
critical value corresponding to the spin depolarization. The variations in the
height of the 0.7 (2e2/h) feature observed in the hole quantum conductance
staircase that is revealed by the p-type silicon quantum wire seem to be
related to the evidences of the quantum conductance staircase obtained by
varying the concentration of electrons in the 1D channel prepared inside the
GaAs-AlGaAs heterojunction.
