Preformed pairs approach to the mass of the charge carrier in YBa2Cu3O 6 + x cuprate

This paper examines how the charge-carrier mass in YBa 2 Cu 3 O 6 + x varies with hole concentration p within the bipolaron framework of high- T c superconductivity. We calculate the three-dimensional polaron mass m p ( p ) and the in-plane polaron mass m p ( p , a b ) across a range of doping levels, incorporating the p -dependent superconducting critical temperature T c ( p ) and mass anisotropy factor γ m 2 = m c ∗ / m a b ∗ . As expected, the behavior of m p ( p ) shows a strong inverse correlation with the superconducting critical temperature, reflecting the relation m p ( p ) ∼ T BEC − 1 ( p ) ≈ T c − 1 ( p ) . In contrast, lattice anisotropy makes the two-dimensional polaron mass increase monotonically with doping. The calculated in-plane polaron masses are compared with theoretical estimates and experimental measurements, showing good consistency at moderate and optimal hole contents. These findings support the usefulness of the preformed-pair concept for understanding the high- T c superconductivity in YBa 2 Cu 3 O 6 + x .