Charge ordering and inter-layer coupling in cuprates

TL;DR

This paper proposes a model for cuprate superconductors where inter-layer Coulomb interactions and charge ordering drive superconductivity, explaining the energy gain and charge dynamics observed experimentally.

Contribution

It introduces a charge ordered bilayer superlattice model where inter-layer Coulomb energy gain supports pairing, linking charge ordering to superconducting energy and properties.

Findings

Electrostatic energy gain along the c-axis correlates with condensation energy.

Charge ordering pattern observed by STM supports the model.

Inter-layer charge complementarity explains the energy scale of $T_c$.

Abstract

We analyze the superconducting state and c-axis charge dynamics of cuprates at optimal doping using a charge ordered bilayer superlattice model in which pairing is supported by inter-layer Coulomb energy gain (potential energy driven superconductivity).The 2D pair-condensate can be characterized by a charge ordered state with a "checkerboard" like pattern seen by scanning tunneling microscopy.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 decrease of the c-axis dielectric screening can be the primary source of the condensation energy below $T_c$. We find that a net gain in the electrostatic energy occurs along the c-axis, which is proportional to the measured condensation energy ($U_0$) and with $T_c$:$E_c^{3D} \approx 2 (\xi_{ab}/a_0+1)^2 U_0 \approx k_B T_c$ and is due to inter-layer charge complementarity (charge asymmetry of the boson condensate) where $\xi_{ab}$ is the coherence length of the condensate and $a_0 \approx 3.9 \AA$ is the in-planelattice constant.