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

Abstract

Higher accuracy low temperature charge transport measurements in combination with precise X-ray diffraction experiment have allowed detecting the symmetry lowering in the single domain Tm 0.19 Yb 0.81 B 12 crystals of the family of dodecaborides with metal-insulator transition. Basing on the fine structure analysis we discover formation of dynamic charge stripes within the semiconducting matrix of Tm 0.19 Yb 0.81 B 12 . The charge dynamics in these metallic nano-size conducting channels is characterized by broad-band optical spectroscopy that allowed estimating the frequency (~2.4•10 11 Hz) of quantum motion of the charge carriers. It is suggested that caused by cooperative Jahn-Teller effect in the boron sub-lattice, the large amplitude rattling

Inhomogeneous superconductivity in LuxZr1−xB12 dodecaborides with dynamic charge stripes

“…Similar gap values Δ 1 (0) ~ 14 K and Δ 2 (0) ~ 8 K were deduced in the rfmeasurements of ZrB 12 [96]. The ratio for the smaller gap was estimated to be only 2Δ 2 /k B T c ~2, and we suppose an essential interband coupling and impurity scattering in these compounds with structural (cooperative JT-effect of B 12 clusters [43]- [45], [87]) and electron (dynamic charge stripes, fig. 1a-1c) instabilities.…”

“…6). A source of lattice instability in LuB 12 and another RE and transition metal dodecaborides is related to the cooperative Jahn-Teller instability of B 12 clusters (ferro-distortive effect), which manifests both the emergence of small static distortions of the fcc lattice and the formation of dynamic charge stripes along unique [110] direction depending from the distribution of impurities and imperfections [42]- [45], [87], [88]. According to the conclusions [43], [44], [87] the infinite cluster of stripes appears only in the disordered phase below T*, but the fcc lattice instability develops in RB 12 with temperature lowering well above T* approaching the Ioffe-Regel limit near T E ~ 150K, where the vibrational density of states reaches the maximum [47] and strong changes appear both in structural parameters and characteristics of the atomic dynamics [44], [88]- [90].…”

“…Taking into account that fast fluctuations of electron density (dynamic charge stripes detected near the RE ions in the fcc lattice of both LuB 12 [42]- [44], [87] and another RE dodecaborides [45], [46]) and that an infinite cluster appears in the disordered cage-glass phase below T* ~ 60 K it seems natural to associate the anisotropy of superconductivity with these inhomogeneities and nanoscale phase separation in the matrix of RB 12 . Moreover, in the filamentary structure the electron density fluctuations with frequency ~240 GHz (~1 meV) [45] are arranged in chains emerging near the RE ions which form channels along <110> directions [43]- [46] and the Cooper pair breaking effect of these dynamic stripes becomes decisive. At low temperatures T < T* the infinite cluster develops and enforces above the percolation threshold (x  x c ~0.23), enhancing the pair breaking and depressing the superconductivity.…”

Evidence of Electronic Phase Separation in the Strongly Correlated Semiconductor YbB12

“…[4] The dynamic charge stripes (ED fluctuations with the frequency 𝜈s ∼ 240 GHz [19] ) were discovered previously in LuB12 at 𝑇 = 50 K, [20] in ZrB12 at 𝑇 ∼ 100 K [21] and in the Tm0.19Yb0.81B12 even at room temperature. [4,22] However, the possibility of existence of these singularities in the parent narrow-gap semiconductor YbB12 has not been investigated up to date.…”

“…1(b)], assuming two energy scales that correspond to the indirect gap 𝐸g/𝑘B ≈ 216 K and to the intragap excitation 𝐸s/𝑘B ≈ 15 K (𝑘B is the Boltzmann constant) estimated from the Hall effect data in accord with the previous results. [1,4,22] Detailed analysis of Hall mobility 𝜇H(𝑇 ) = 𝑅H(𝑇 )/𝜌(𝑇 ) will be presented elsewhere. The two regimes I and II are separated in YbB12 by the strong peak at 𝑇s ∼ 15 K on the 𝜇H(𝑇 ) curve [Fig.…”