Double-Bridge Mechanism for Enhancing Tc in Oxide Superconductors

We propose a new double-bridge mechanism to significantly enhance $T_c$ in ionic oxide superconductors. Based on our recently proposed ionic-bond-driven O/Cu-bridged (bridge-I) pairing e${}^{-}$-O-e${}^{-}$/h${}^{+}$-Cu-h${}^{+}$ formed in the pseudogap phase ($T_c<T<T^{\ast }$), we reveal a key bridge-II Cu/O-mediated inter-pair attraction that overcomes direct Coulomb repulsion and drives coherent Bose-Einstein condensation (BEC) of preformed Cooper pairs. Within the BEC framework (Eq.(3)), $T_c$ follows the Uemura scaling $(n_{\mathrm{p}\mathrm{a}\mathrm{i}\mathrm{r}}^{3\mathrm{D}}{)}^{2\mathrm{/}3}\mathrm{/}{m}_{\mathrm{p}\mathrm{a}\mathrm{i}\mathrm{r}}^{\ast }$ or $n_{\mathrm{p}\mathrm{a}\mathrm{i}\mathrm{r}}^{2\mathrm{D}}\mathrm{/}{m}_{\mathrm{p}\mathrm{a}\mathrm{i}\mathrm{r}}^{\ast }$ and increases linearly with the attractive scattering length $a<0$. Strengthening bridge-II attraction, minimizing $m_{\mathrm{p}\mathrm{a}\mathrm{i}\mathrm{r}}^{\ast }$, and optimizing $n_{\mathrm{p}\mathrm{a}\mathrm{i}\mathrm{r}}^{3\mathrm{D}}$ are the key to maximizing $T_c$. This double-bridge mechanism unifies the $\mathbf{\text{eV-scale}}$ strong pairing at room temperature and BEC, provides a universal route toward higher $T_c$, and guides the design of next-generation superconductors.