Bipolaronic High-Temperature Superconductivity

Electron-lattice interactions play a prominent role in quantum materials, making deeper understanding of direct routes to phonon-mediated high-transition-temperature ($T_{\mathrm{c}}$) superconductivity desirable. However, it has been known for decades that weak electron-phonon coupling gives rise low values $T_{\mathrm{c}}$, while strong leads lattice instability or formation bipolarons, generally assumed be detrimental superconductivity. Thus, the route high-$T_{\mathrm{c}}$ materials from mechanisms heretofore appeared limited raising phonon frequency as hydrogen sulfides. Here we present simple model based on superfluidity light bipolarons. In contrast widely studied Holstein where distortions modulate electron's potential energy, investigate situation electron hopping. This physics small-size, yet which study using an exact sign-problem-free Monte Carlo approach, demonstrating new high-$T_\mathrm{c}$ We find $T_\mathrm{c}$ our generically and significantly exceeds typical upper bounds Migdal-Eliashberg theory The key ingredient this bipolaronic mechanism high is combination mass small size Our work establishes principles towards design superconductors via functional material engineering.