Spin-Conserving Resonant Tunneling in Twist-Controlled WSe-hBN-WSe Heterostructures.

We investigate interlayer tunneling in heterostructures consisting of two tungsten diselenide (WSe) monolayers with controlled rotational alignment, and separated by hexagonal boron nitride. In samples where the two WSe monolayers are rotationally aligned we observe resonant tunneling, manifested by a large conductance and negative differential resistance in the vicinity of zero interlayer bias, which stem from energy- and momentum-conserving tunneling. Because the spin-orbit coupling leads to coupled spin-valley degrees of freedom, the twist between the two WSe monolayers allows us to probe the conservation of spin-valley degree of freedom in tunneling. In heterostructures where the two WSe monolayers have a 180° relative twist, such that the Brillouin zone of one layer is aligned with the time-reversed Brillouin zone of the opposite layer, the resonant tunneling between the layers is suppressed. These findings provide evidence that, in addition to momentum, the spin-valley degree of freedom is also conserved in vertical transport.