Optical study of the gap formation and low-energy excitations in YbB12

Low-temperature infrared spectroscopy of the strongly correlated semiconductor Tm0.19Yb0.81B12with dynamic charge stripes

“…We associate its origin with the vibrationally coupled localized states [27] near the bottom of the conduction band. These peaks are well-known from previous optical studies of YbB 12 where the broad bump which appears on cooling in the range 300-700 K [33] was described by one Lorentzian located at ∼1600-2000 cm −1 (0.2-0.25 eV) depending on the temperature [30,[33][34][35][36][37][38]. In [30,[33][34][35][36][37][38] the authors have also discovered a shoulder in the σ(ν) spectrum located near 40 meV, just on the verge of the energy gap in the density of states (DOS) of YbB 12 .…”

“…These peaks are well-known from previous optical studies of YbB 12 where the broad bump which appears on cooling in the range 300-700 K [33] was described by one Lorentzian located at ∼1600-2000 cm −1 (0.2-0.25 eV) depending on the temperature [30,[33][34][35][36][37][38]. In [30,[33][34][35][36][37][38] the authors have also discovered a shoulder in the σ(ν) spectrum located near 40 meV, just on the verge of the energy gap in the density of states (DOS) of YbB 12 . Similar excitation can be seen in the spectra of Tm 0.19 Yb 0.81 B 12 where the corresponding band is represented by a combination of L4 + L5 peaks (see figures 1(b) and (c)).…”

“…There are several low-frequency absorption peaks in the spectra of Tm 0.19 Yb 0.81 B 12 crystal, denoted as L1, L2 and L3 (see figures 1(b) and (c)), that were not detected previously in Yb 1−x Lu x B 12 [30,[33][34][35][36][37][38]. We suggest, that these are collective excitations that involve both, the lattice vibrations and the conduction electron dynamics, as is discussed in the analysis presented below.…”