Possible Proximity Effect in Graphene/$\alpha$-RuCl$_3$ Layered Heterostructure

Recently, the layered antiferromagnetic Mott insulator $\alpha$-RuCl$_3$ has been studied in bulk crystals and found to be proximate to a Kitaev quantum spin liquid. Since the QSL is primarily a two-dimensional phenomenon, it may be possible to stabilize the QSL phase in exfoliated single- or few-layer $\alpha$-RuCl$_3$. We performed DC transport measurement on exfoliated $\alpha$-RuCl$_3$ flakes of various thicknesses and found the resistance to freeze out above 30 K, well above the N\'eel temperature. To access the low temperature regime with transport, we fabricated van der Waals heterostructure consisting of graphene and $\alpha$-RuCl$_3$ layers in close proximity. The graphene resistance is found to show an unusually strong temperature dependence compared to graphene on SiO$_2$. More strikingly, a ``kink'' in the resistance centered at 20 K is observed, close to the onset of antiferromagnetic ordering in $\alpha$-RuCl$_3$.