Superheavy nuclei represent the extreme atoms and nuclides known at the limit of mass and charge. The observed superheavy nuclei are all proton-rich; they decay primarily by emitting $\alpha$ particles and by fission with a possible small electron capture (EC) branch. Due to the huge atomic numbers and associated relativistic effects, EC decays of superheavy systems are expected to differ from what is known in lighter nuclei. In this letter, using the quantified relativistic nuclear density functional theory and the quasiparticle random-phase approximation with the interaction optimized to experimental $\mathrm{EC}/{\beta }^{\pm }$-decay half-lives, and Gamow-Teller resonance energies, we study the $\mathrm{EC}/{\beta }^{\pm }$ decays in $Z=101–118$ nuclei. Both allowed ($1^{+}$) and first-forbidden ($0^{-},1^{-}$ and $2^{-}$) transitions are considered. We show that the first-forbidden $1^{-}$ transitions dominate the decay rates in almost all studied nuclei. For proton-rich nuclei, EC dominates over ${\beta }^{+}$ decay. Based on calculations with two relativistic energy density functionals, we identify 45 candidate nuclei in which a competition between weak decays and $\alpha$ decay and spontaneous fission is expected.

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• Beta decay
• Electron & muon capture
• Nuclear structure & decays
• Synthesis of new superheavy elements
• A ≥ 220
• Density functional theory
• Random phase approximation