Optical clock sensitive to variation of the fine structure constant   based on the Ho$^{14+}$ ion
  We study the Ho$^{14+}$ ion as a candidate for extremely accurate and stable optical atomic clock which is sensitive to the time variation of the fine structure constant. We demonstrate that the proposed system has all desired features including relatively strong optical electric dipole and magnetic dipole transitions which can be used for cooling and detection. Zero quadrupole moments for the relevant states in the clock transition allows interrogating multiple ions to improve the clock stability. 
V. A. Dzuba, V. V. Flambaum, and Hidetoshi Katori
physics.atom-ph