Explain Tc variation among cuprates with ostensibly identical CuO2-plane physics

Determine the physical origin of the substantial differences in superconducting transition temperatures Tc among La2−xSrxCuO4 (La214), YBa2Cu3O7−δ (Y123), and HgBa2Ca2Cu3O8+z (Hg1223), despite these materials sharing similar CuO2-plane electronic physics.

Background

The paper measures in-plane optical reflectivity and conductivity of Bi2223 and compares pseudogap-related features across single-, double-, and triple-layer cuprates. A key empirical observation is a doping-insensitive gap-like conductivity peak whose energy correlates with the optimal Tc across different cuprate families.

In the concluding discussion, the authors note that standard explanations—such as disorder, lattice distortions, and competing orders—do not satisfactorily account for the large differences in Tc observed across La214, Y123, and Hg1223, even though these compounds share the central CuO2-plane physics. This motivates an explicit open question about the underlying cause of the Tc variation.