Magnetotransport in Graphene/Pb_0.24Sn_0.76Te Heterostructures: Finding a Way to Avoid Catastrophe

Abstract

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 Pb1-xSnxTe (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/(V s) and a magnetoresistance approaching 100%, 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/nonpolar interface interaction. Our results suggest that proximity induced interface states with hybrid properties can be added to the still growing list of behaviors in these materials.

Spintronic Quantum Phase Transition in a Graphene/Pb0.24Sn0.76Te Heterostructure with Giant Rashba Spin‐Orbit Coupling

“…However, SnTe was mainly used to approximate PbSnTe due to the expense of the calculations. Additional details can be found in the Supporting Information or in the previous work in reference 21, where it was demonstrated that SnTe, PbTe, and PbSnTe all behave similarly in this context, where the dominant heterostructure behavior was from a meeting of polar and non-polar surfaces.…”

“…Pb 0.24 Sn 0.76 Te (111) (PST) topological crystalline insulator (TCI) films were grown to a thickness of 7 nm on GaAs (001) by molecular beam epitaxy using methods described previously. [21] The stoichiometry was chosen to maximize the bulk bandgap while maintaining the TCI behavior, as discussed in depth elsewhere. [21,22] Graphene was grown by low pressure (5-50 mTorr) chemical vapor deposition on copper foiled at 1030 °C under flowing H 2 and CH 4 gas.…”

“…[21] The stoichiometry was chosen to maximize the bulk bandgap while maintaining the TCI behavior, as discussed in depth elsewhere. [21,22] Graphene was grown by low pressure (5-50 mTorr) chemical vapor deposition on copper foiled at 1030 °C under flowing H 2 and CH 4 gas. After growth, the Cu substrates were etched and transferred to the PbSnTe using a wet process.…”

“…where h is Planck's constant, e is the elementary charge, P FM is the polarization of the ferromagnetic detector contact (∼48% for Ni 80 Fe 20 ), [49] v F is the Fermi velocity, m * is the effective mass, W is the width of the channel, p Rashba is the induced spin polarization due to the Rashba effect, and m u is a unit vector along the direction of magnetization. [21] In previous studies, spontaneous, nonequilibrium spin polarization due to either the Rashba effect or topological surface state spin-momentum locking is distinguishable by having opposite signs in the vector p Rashba . However, as many others have noted, [34,45,49] it is difficult to draw any conclusions about the sign of the polarization.…”

“…The previous theory work on the Gr/PST heterostructure demonstrated that time reversal symmetry is broken here, resulting in the destruction of the topological state in the PST. [21] For a trivial 2DEG with parabolic energy dispersion, spin-momentum locking, a manifestation of spontaneous nonequilibrium spin polarization caused by an electric current, arises due to Rashba spinorbit coupling (SOC). [36,37] This is the same effect that allows a measure of control over spin relaxation using an electric field because the spin-splitting energy is proportional to the expectation value of electric field.…”