  Topological insulators (TIs) are emerging materials for next-generation
low-power nanoelectronic and spintronic device applications. TIs possess
non-trivial spin-momentum locking features in the topological surface states in
addition to the spin-Hall effect (SHE), and Rashba states due to high
spin-orbit coupling (SOC) properties. These phenomena are vital for observing
the charge-spin conversion (CSC) processes for spin-based memory, logic and
quantum technologies. Although CSC has been observed in TIs by potentiometric
measurements, reliable nonlocal detection has so far been limited to cryogenic
temperatures up to T = 15 K. Here, we report nonlocal detection of CSC and its
inverse effect in the TI compound Bi1.5Sb0.5Te1.7Se1.3 at room temperature
using a van der Waals heterostructure with a graphene spin-valve device. The
lateral nonlocal device design with graphene allows observation of both
spin-switch and Hanle spin precession signals for generation, injection and
detection of spin currents by the TI. Detailed bias- and gate-dependent
measurements in different geometries prove the robustness of the CSC effects in
the TI. These findings demonstrate the possibility of using topological
materials to make all-electrical room-temperature spintronic devices.
