Emergence of the Isotropic Kitaev Honeycomb Lattice with Two dimensional Ising Universality in $\alpha $\textbf{-RuCl}$_{\mathrm{\mathbf{3}}}$

The Quantum Spin Liquid(QSL) state is indeed exactly derived by fractionalizing the spin excitation into spinless Majorana fermions in a perfect two-dimensional (2D) honeycomb lattice, so-called Kitaev lattice, and its experimental realization is eagerly being pursued. Here we report the Kitaev lattice stacking with van der Waals (vdW) bonding in a high quality $\alpha $-RuCl3 crystal using x-ray and neutron diffractions. Even in absence of apparent monoclinic distortion, the system exhibits antiferromagnetic (AFM) ordering below 6.5 K, likely due to minute magnetic interaction from trigonal distortion and/or interlayer coupling additionally to the Kitaev Hamiltonian. We also demonstrate 2D Ising-like critical behaviors near the Néel temperature in the order parameter and specific heat, capturing the characteristics of short range spin-spin correlations underlying the Kitaev model. Our findings hold promise for unveiling enigmatic physics emerging from the Kitaev QSL.