Two-Gap Superconductor ZrB12 with Dynamic Stripes and Charge Density Waves: Crystal Structure, Physical Properties, and Pairing Mechanism

A review of long-term studies of the ZrB12 and LuB12 superconductors with very similar conduction bands and phonon spectra, but with radically different (by a factor of 15–20) critical temperatures and magnetic fields is presented. A detailed analysis of well-known studies in combination with new results of the structural, thermodynamic, and charge transport measurements obtained here for these metallic dodecaborides with Jahn–Teller instability of the rigid boron network and with dynamic charge stripes allows us to conclude in favor of the primary role of nanoscale effects of electron phase separation, leading to the formation of one-dimensional dynamic chains with different configurations of fluctuating charges, which in the case of ZrB12 are predominantly 2p states, and for LuB12—5d–2p states. We propose a new vibron–plasmon–phonon pairing mechanism in ZrB12, which may be common to different classes of high-Tc superconductors.