Temperature dependence of Peierls-Hubbard phase transition in [Pd(cptn)2Br]Br2 studied by scanning tunneling microscopy

The temperature dependence of the Peierls-Hubbard phase transition in [Pd(cptn)₂Br]Br₂ (cptn: 1R,2R-diaminocyclopentane) was directly observed using a low- Temperature scanning tunneling microscope. A short ligand without alkyl chains was used to form a rigid crystal lattice to reduce the effect of structural changes in the crystal with temperature. The hysteresis in the temperature dependence of the ratio between the areas of the charge density wave (CDW) state produced by the Pd^II-Pd^IV mixed-valence state and the Mott-Hubbard (MH) state with a PdIIIaveraged valence state which is a characteristic of the first-order phase transition, was directly observed at the atomic scale. Pinning of the CDW phase by defects was observed below the critical temperature, suggesting the growth of the CDW phase with defects as nuclei.