Spin to charge conversion in van der Waals heterostructures

Graphene has been known as an excellent material for long-distance spin transport due to its weak spin-orbit coupling (SOC). However, the same reason makes graphene an adverse candidate for different spintronics applications in which strong SOC is required, such as the Datta and Das spin transistor proposal or spin-charge interconversions. It has recently been predicted theoretically that SOC can be induced in graphene so that exotic spin-orbit phenomena such as spin Hall effect (SHE) or Rashba-Edelstein effect can be obtained. In our work, by using van der Waals heterostructure-based lateral spin valves, we experimentally demonstrate spin-to-charge conversion (SCC) due to SHE in graphene via spin-orbit proximity with MoS₂, a transition metal dichalcogenide (TMD)^1,2. The combination of long-distance spin transport and large spin-to-charge conversion in a van der Waals heterostructure gives rise to a hitherto unreported efficiency for the spin-to-charge voltage output. We performed similar experiments in graphene in proximity with WSe₂. Here we observed gate-tunable SHE with SCC efficiency larger than in some of the best SCC materials such as topological insulators. Using a similar approach, we observed large multidirectional SCC in Weyl semimetal MoTe₂³. Here, due to the low symmetry of MoTe₂ crystal, we detect, along with the conventional SCC, an unconventional SCC where the spin polarization and the charge current are parallel. Our finding enables the simultaneous conversion of spin currents with any in-plane spin polarization in one single experimental configuration. All in all, these exceptional effects obtained by the unique properties of 2D materials open exciting opportunities in a variety of future spintronic applications.

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