Two-dimensional superconductivity and topological states in PdTe2 thin films

We report on a bottom-up approach via molecular-beam epitaxy to grow high-quality crystalline two-dimensional films of ${\mathrm{PdTe}}_{2}$ on ${\mathrm{SrTiO}}_{3}$(001), and investigation on the electronic and superconducting properties therein by using scanning tunneling microscopy and transport experiments in combination with first-principles calculations. We observed a transition from the narrow-gap semiconducting phase in the monolayer to the metallic phase in the multilayer films. Importantly, all the multilayer films exhibited robust superconductivity, whose transition temperatures in the ultrathin limit were obviously higher than expected from the empirical inverse-of-thickness dependence and could be further enhanced through magnesium intercalation. Our first-principles studies revealed thickness-tuned band topology caused by the significant orbital-dependent interlayer coupling, which explained the experimentally observed thickness-dependent behaviors of atomic and electronic properties. Combined with the prediction of topologically nontrivial states introduced by honeycomb lattice of $p$ orbitals, ${\mathrm{PdTe}}_{2}$ thin films are promising material candidates for exploring the interplay between superconductivity and topology in the two-dimensional limit.