  While heterostructures are ubiquitous tools enabling new physics and device
functionalities, the palette of available materials has never been richer.
Combinations of two emerging material classes, two-dimensional materials and
topological materials, are particularly promising because of the wide range of
possible permutations that are easily accessible. Individually, both graphene
and Pb0.24Sn0.76Te (PST) are widely investigated for spintronic applications
because graphene's high carrier mobility and PST's topologically protected
surface states are attractive platforms for spin transport. Here, we combine
monolayer graphene with PST and demonstrate a hybrid system with properties
enhanced relative to the constituent parts. Using magnetotransport
measurements, we find carrier mobilities up to 20,000 cm2/Vs and a
magnetoresistance approaching 100 percent, greater than either material prior
to stacking. We also establish that there are two distinct transport channels
and determine a lower bound on the spin relaxation time of 4.5 ps. The results
can be explained using the polar catastrophe model, whereby a high mobility
interface state results from a reconfiguration of charge due to a
polar/non-polar interface interaction. Our results suggest that proximity
induced interface states with hybrid properties can be added to the still
growing list of remarkable behaviors in these novel materials.
