Metal-chalcogen bond-length induced electronic phase transition from semiconductor to topological semimetal in ZrX2 (X=Se and Te)

Topological transition-metal dichalcogenides have been the center of research interests in materials science, recent days, due to their potential applications in spintronics, optoelectronics, and quantum computations. In this paper, using angle resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations, we systematically studied the low-energy electronic structure of bulk ZrTe2. ARPES studies on ZrTe2 demonstrate free charge carriers at the Fermi level, which is further confirmed by the DFT calculations. An equal hole and electron carrier density estimated from the ARPES data points to ZrTe2 being a semimetal. The DFT calculations further suggest a band inversion between Te p and Zr d states at the Gamma point, hinting at the nontrivial band topology in ZrTe2. Thus our studies suggest that ZrTe2 is a topological semimetal. Also, a comparative band structure study is done on ZrSe2, which shows a semiconducting nature of the electronic structure with an indirect band gap of 0.9 eV between Gamma(A) and M(L) high-symmetry points. Below we show that the metal-chalcogen bond length plays a critical role in the electronic phase transition from a semiconductor to a topological semimetal ingoing from ZrSe2 to ZrTe2.