Revealing Symmetry-broken Superconducting Configurations by Density Functional Theory

A coherent theory for both conventional and unconventional superconductors is currently lacking. Here we show that the electron charge densities of Al, YBa2Cu3O7 (YBCO), and LaH10 along with Pb and Nb3Sn share the same feature of electron charge gains in their respective superconducting configurations (SCCs) predicted by first-principles calculations based on the density functional theory (DFT). It is discovered that the formation of SCCs is due to the local symmetry breaking from their normal conducting configurations (NCCs), and the electron charge gains in SCCs form electron tunnels in crystals that resemble pontoons, thus termed as electron pontoon tunnel (EPT) here. The nuclei promoting the formation of EPTs in conventional superconductors have strong bonding with other nuclei, resulting in their EPTs easily destroyed and thus low superconducting critical temperature (Tc), while in unconventional superconductor, this bonding is very weak as shown by negative stretching force constants in YBCO, thus resulting in much higher Tc. The fundamental understanding of SCCs and the capability to predict them by DFT enable theoretical search of room temperature superconductors without empirical models.