Prof. Gun-Do Lee, Seoul National University

Although many years have passed since the discovery of high-critical temperature (high-T_c) superconducting materials, the underlying mechanism is still unknown. In particular, the intricate interplay between non-ergodic bad metals and strange metals in high-T_c superconductors has remained enigmatic. Intriguingly, most of these unconventional high-T_c superconductors have layered structures. Using ab initio molecular dynamics (AIMD) simulations coupled with the temperature-dependent effective potential (TDEP) method, we successfully reproduce B1g phonon anomaly in YBCO, a representative material of unconventional high-T_c layered superconductors. We discovered an interlayer thermal decoupling which is driven by Ba atoms in YBCO. Surprisingly, we found that the thermal decoupling solves the linear-T resistivity in the strange metal phase, which has been a major mystery in unconventional high-T_c superconductors. It is revealed that the thermal decoupling can also explain the Uemura relation and superconducting dome rigorously and quantitatively. The strange metal and Uemura relation are tightly coupled by thermal decoupling. Thermal decoupling is also a key factor in understanding the relationship between the superconductivity and flat bands found in magic-angle twisted bilayer graphene. The relation between thermal decoupling and quantum geometry will be mentioned. Our discoveries will offer a revolutionary perspective on high-T_c superconductivity, suggesting the potential for a transformative shift in our comprehension.