Pair condensation and inter-layer coupling in cuprates pairing on a superlattice.pdf

a r X i v : c o n d - m a t / 0 2 0 5 1 9 4 v 5 [ c o n d - m a t .s u p r - c o n ] 2 7 N o v 2 0 0 2 Charge ordering and inter-layer coupling in cuprates P. Su?le Research Institute for Technical Physics and Material Science, Konkoly Thege u. 29-33, Budapest, Hungary, sule@mfa.kfki.hu (February 6, 2008) We analyze the superconducting state and c-axis charge dynamics of cuprates using a charge or- dered bilayer superlattice model in which pairing is supported by inter-layer Coulomb energy gain (potential energy driven superconductivity). The superlattice nature of high-Tc superconductivity is experimentally suggested by the smallness of the in-plane coherence length ξab ≈ 10? 30A? which is comparable with a width of a 3a0 × 3a0 to 8a0 × 8a0 (a0 ≈ 3.9A?) square supercell lattice layer. The 2D pair-condensate can be characterized by a charge ordered state with a ”checkerboard” like pattern seen by scanning tunneling microscopy. The 2D ? 3D quantum phase transition of the hole-content at Tc, supported by c-axis optical measurements, is also studied. The pair condensation might lead to the sharp decrease of the normal state c-axis anisotropy of the hole content and hence to the decrease of inter-layer dielectric screening. The drop of the c-axis dielectric screening can be the primary source of the condensation energy below Tc. We find that a net gain in the electrostatic energy occurs along the c-axis, which is proportional to the measured condensation energy (U0) and with Tc: E 3D c ≈ 2N 2U0 ≈ kBTc and is due to inter-layer charge complementarity (charge asymmetry of the boson condensate) where N is the real space period of the condensate. The bilayer model naturally leads to the effective mass of m? ≈ 4me found by experiment. The static c-axis dielectric constant ?c is calculated for various cuprates and compared with the available experimental data. We find correlation between Tc and the inter-layer spacing d, ?c and with the coherence area of the condensat