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 x 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.

Automated summary

Using first-principles calculations, we find that 1T-HfTe2 shows stable 2 x 2 CDW order in its monolayer form due to enhanced electron-phonon coupling. The CDW induces metal-to-insulator transition and the suppression of CDW by electron doping leads to Ising superconductivity in centrosymmetric monolayer 1T-HfTe2, protected by spin-orbital locking. These results provide new insights for designing and controlling quantum states in two-dimensional matter.