Observation of dynamic charge stripes in Tm_0.19Yb_0.81B₁₂ at the metal–insulator transition

Accurate low temperature charge transport measurements in combination with high-precision x-ray diffraction experiments have allowed detection of the symmetry lowering in the single domain Tm_0.19Yb_0.81B₁₂ crystals that belong to the family of dodecaborides with metal–insulator transition. Based on the fine structure analysis we discover the formation of dynamic charge stripes within the semiconducting matrix of Tm_0.19Yb_0.81B₁₂. The charge dynamics in these conducting nano-size channels is characterized by broad-band optical spectroscopy that allowed estimating the frequency (∼2.4 × 10¹¹ Hz) of quantum motion of the charge carriers. It is suggested that cooperative Jahn–Teller effect in the boron sublattice is a cause of the large-amplitude rattling modes of the Tm and Yb ions responsible for the 'modulation' of the conduction band along one of the directions through the variation of 5d-2p hybridization of electron states. (paper)