Emergence of charge density wave and Ising superconductivity in centrosymmetric monolayer 1T-HfTe₂

Understanding and control of many-body collective phenomena such as charge density wave (CDW) and superconductivity in atomically thin crystals remains a hot topic in material science. Here, using first-principles calculations, we find that 1T-HfTe₂ possessing no CDWs in the bulk form, unexpectedly shows a stable 2 × 2 CDW order in the monolayer form, which can be attributed to the enhancement of electron–phonon coupling (EPC) in the monolayer. Meanwhile, the CDW induces a metal-to-insulator transition in monolayer 1T-HfTe₂ through the accompanying lattice distortion. Remarkably, Ising superconductivity with a significantly enhanced in-plane critical field can emerge in centrosymmetric monolayer 1T-HfTe₂ after the CDW is suppressed by electron doping. The Ising paring is revealed to be protected by the spin–orbital locking without the participation of the inversion symmetry breaking which is a must for conventional 2H-NbSe₂-like Ising superconductors. Our results open a new window for designing and controlling novel quantum states in two-dimensional (2D) matter.