We study atomic systems that are in the frequency range of optical atomic clocks and have enhanced sensitivity to potential time variation of the fine-structure constant $\alpha$. The high sensitivity is due to coherent contributions from three factors: high nuclear charge $Z$, high ionization degree, and significant differences in the configuration composition of the states involved. Configuration crossing keeps the frequencies in the optical range despite the large ionization energies. We discuss a few promising examples that have the largest $\alpha$ sensitivities seen in atomic systems.

• Received 8 July 2010

DOI:https://doi.org/10.1103/PhysRevLett.105.120801