Signatures of Band Gap Inversion and Topological Transition in Core-Shell GaAs-Pb_1-xSn_xTe Nanowires.

Topological Crystalline Insulators (TCIs) are a novel class of quantum materials, distinguished by robust surface states protected not by time-reversal(T), but crystal symmetry. This phenomenon was studied in bulk and thin film IV-VI materials such as SnTe, Pb_1-xSn_xTe and Pb_1-xSn_xSe.

We study semiconductor core-shell nanowires consisting of GaAs core and thin Pb_1-xSn_xTe shell, both grown by molecular beam epitaxy. The shells are deposited on GaAs core nanowires (inclined about 35 deg to the Si(001) substrate surface plan), covering 2—3 of their facets . We measure transport through Pb_1-xSn_xTe shells in temperature range of 1.7 -- 300K and in perpendicular magnetic fields up to 12T.

We find a resistivity minimum around 150K, and analyze it in the context of bandgap closing and reopening for a particular composition of Pb_1-xSn_xTe. We study magnetoresistance at low temperatures <10K, which exhibits aperiodic oscillations on the scale of 1-2 T with a minimum or maximum, discussing possible origins of the effect.