  Determining the symmetry breaking order of correlated quantum phases is
essential for understanding the microscopic interactions in their host systems.
The flat bands in magic angle twisted bilayer graphene (MATBG) provide an
especially rich arena to investigate such interaction-driven ground states, and
while progress has been made in identifying the correlated insulators and their
excitations at commensurate moire filling factors, the spin-valley
polarizations of the topological states that emerge at high magnetic field
remain unknown. Here we introduce a new technique based on twist-decoupled van
der Waals layers that enables measurements of their electronic band structure
and, by studying the backscattering between counter-propagating edge states,
determination of relative spin polarization of the their edge modes. Applying
this method to twist-decoupled MATBG and monolayer graphene, we find that the
broken-symmetry quantum Hall states that extend from the charge neutrality
point in MATBG are spin-unpolarized at even integer filling factors. The
measurements also indicate that the correlated Chern insulator emerging from
half filling of the flat valence band is spin-unpolarized, but suggest that its
conduction band counterpart may be spin-polarized. Our results constrain models
of spin-valley ordering in MATBG and establish a versatile approach to study
the electronic properties of van der Waals systems.
