Electronic and transport properties of the Te-defect lattice in DyTe1.8

The rare-earth ditellurides are known to form a two-dimensional square lattice where the strong Fermi surface nesting leads to structural modulation. In contrast to charge density waves, the supercell modulation is accompanied by the formation of the periodic Te vacancy network, where the Te deficiency affects the nesting vector, i.e., the supercell size, via tuning the chemical potential. In this work, first-principles electronic-structure calculations for the $\sqrt{5}\ifmmode\times\else\texttimes\fi{}\sqrt{5}$ supercell, which commonly appears in this family of tellurides, reveal interesting electronic and transport properties of the Te defect lattice in ${\mathrm{DyTe}}_{1.8}$. The reconstruction of the Te-deficient square lattice, consisting of a single Te dimer and a pair of Te trimers per unit cell, gives rise to an out-of-plane polarization, whose direction depends on the position of the dimer. This results in various close-in-energy parallel and antiparallel polarization configurations of successive Te layers depending on the dimer positions. We predict that the orientation of the Te dimers, and hence the corresponding structural motifs, can be reversibly switched between two in-plane perpendicular directions under tensile epitaxial strain via a piezoelectric substrate, resulting in a colossal conductivity switching. Furthermore, the Te-dimer orientations result in an asymmetric Fermi surface, which can be confirmed by quantum oscillations measurements.