Although many years have passed since the discovery of 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 the B_1g phonon anomaly in YBCO, a representative material of unconventional high-T_c layered superconductors. We discovered interlayer thermal decoupling driven by Ba atoms in YBCO. Surprisingly, we found that thermal decoupling resolves 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 rigorously and quantitatively explain the Uemura relation and superconducting dome [1]. The strange metal and Uemura relation are tightly coupled by thermal decoupling. Thermal decoupling is also a key factor in understanding the relationship between superconductivity and flat bands found in magic-angle twisted bilayer graphene. The relation between thermal decoupling and quantum geometry will be mentioned. We also found thermal decoupling in CsV₃Sb₅ Kagome superconductors. The relation between the charge density wave and the suppression of T_c can be explained through thermal decoupling. Our discoveries will offer a revolutionary perspective on high-T_c superconductivity, suggesting a transformative shift in our understanding.

[1] S. Lee et al. Materials Today Physics 59, 101916 (2025)