Mechanical stacking of two dissimilar materials often has surprising consequences for heterostructure behavior. In particular, a two-dimensional electron gas (2DEG) is formed in the heterostructure of the topological crystalline insulator Pb0.24Sn0.76Te and graphene due to contact of a polar with a nonpolar surface and the resulting changes in electronic structure needed to avoid polar catastrophe. We study the spintronic properties of this heterostructure with non-local spin valve devices. We observe spin-momentum locking at lower temperatures that transitions to regular spin channel transport only at ~40 K. Hanle spin precession measurements show a spin relaxation time as high as 2.18 ns. Density functional theory calculations confirm that the spin-momentum locking is due to a giant Rashba effect in the material and that the phase transition is a Lifshitz transition. The theoretically predicted Lifshitz transition is further evident in the phase transition-like behavior in the Landé g-factor and spin relaxation time.

Topological materials, such as Cd3As2, are of great importance for next-generation computing systems where energy efficiency is paramount. For example, in spin–orbit torque magnetic access memory (SOT-MRAM), topological materials generate the spin–orbit torque necessary for magnetization switching of an adjacent magnetic layer. Current shunting at the ferromagnet–topological material interface can be detrimental for spin generation and overall SOT efficiency. Here, the current shunting effect is analyzed in permalloy- and gold-shunted Cd3As2 disk structures using angle-dependent magnetoresistance measurements. We observe Shubnikov–de Haas oscillations and weak antilocalization. Hakami–Larkin–Nagaoka and Tkachov–Hankiewicz models are used to evaluate the weak antilocalization. We confirm the effects of current shunting and discuss its detriment to the efficiency of spin-based devices.

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.

Topological insulators (TIs) are promising candidates for alternative computing device designs. In particular, they have great potential for spintronic devices, where utilization of electron spin rather than charge would allow for lower-power and higher-performance computing in next-generation architectures. Efficient conversion between spin and charge signals is crucial to spintronic technology. TIs provide highly efficient spin-to-charge conversion, as a result of their unique topological properties. One way to electrically quantify conversion efficiency is with the spin Hall effect (SHE). Here, we present SHE measurements of the topological insulator Bi2Te2.5Se0.5. Because of the topological nature of this material, we can measure the SHE without the use of ferromagnetic injectors or detectors. Using the nonlocal resistance, we measure spin Hall angles up to 2.4 with spin lifetimes up to 9 ps. Furthermore, ferromagnet-free measurement allows for quick diagnostics of the spin properties without the need to fabricate multilevel devices.

Bi2Se3, widely studied as a topological insulator, has great potential for applications in low-power electronics and quantum computing. Intrinsic doping, however, presents a persistent challenge, leading to predominantly bulk conduction. In this work, we use substitutional Sn dopants to control the Fermi level in Bi(2)Se(3 )films. Scanning tunneling microscopy (STM) shows a shift in the local density of states toward the Dirac point as more Sn is incorporated. Density functional theory calculations elucidate the STM results, showing that Sn adds metallic states near the Fermi level that are localized to the defect sites while leaving the Dirac cone undisturbed. Electronic transport measurements demonstrate that the Sn defects increase the separation between bulk and surface states, though bulk conduction remains a dominant component.