  We have studied the strongly interacting, two-valley two-dimensional (2D)
electron system in ultrahigh mobility SiGe/Si/SiGe quantum wells in parallel
magnetic fields strong enough to completely polarize the electron spins thus
making the electron system "spinless". It occurs that the metallic temperature
dependence of the resistivity, although weaker than that in the absence of
magnetic field, still remains strong even when the spin degree of freedom is
removed. Several independent methods have been used to establish the existence
of the genuine MIT in the spinless two-valley 2D system. This is in contrast to
the previous results obtained on more disordered silicon samples, where the
polarizing magnetic field causes a complete quench of the metallic temperature
behavior.
