Concomitant charge-density-wave and unit-cell-doubling structural transitions inDy5Ir4Si10

Abstract

The tetragonal rare-earth transition-metal silicide system with three-dimensional crystallographic structure ${R}_{5}{T}_{4}{\mathrm{Si}}_{10}$, where $R$ is Dy, Ho, Er, Tm, and Lu, and $T\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}\mathrm{Ir}$ and Rh, has been shown to exhibit fascinating charge-density-wave (CDW) phase transitions, a phenomenon largely found in otherwise low-dimensional systems. In this study, we report the investigations of CDW in Dy${}_{5}$Ir${}_{4}$Si${}_{10}$ at different temperatures using transmission electron microscopy techniques including electron diffraction and dark-field imaging. Incommensurate superlattice spots along the $c$ axis were observed in the electron-diffraction patterns when the sample was cooled below the CDW transition temperature at $\ensuremath{\sim}$208 K. CDW becomes commensurate with further cooling and configurations of CDW dislocations convincingly show that the CDW phase transition is accompanied by a concomitant cell-doubling crystallographic structural phase transition. Intriguingly, the cell-doubling transition is featured by a broken inversion symmetry along the $c$ axis and a disparity in the CDW-modulation vectors with opposite signs, which gives rise to two sets of CDW domains with reversed contrasts. The profound physics underlining this notable domain-contrast behavior is discussed.