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Description
The spin-ladder cuprate Sr14-x Cax Cu24 O41 is the only known ladder cuprate superconductor, exhibiting a maximum superconducting transition temperature of approximately Tc=9 K under an applied pressure of 4.5 GPa. Prior to the onset of superconductivity, the material exhibits increasingly two-dimensional electronic behavior as inter-ladder coupling strengthens. Negative charge-transfer energies (Δdp<0), corresponding to the regime associated with the proposed copper valence transition, are expected to further enhance inter-ladder coupling, motivating the study of larger coupled-ladder systems. This work employs the Constrained Path Quantum Monte Carlo (CPQMC) algorithm to investigate the electronic properties of coupled CuO ladder systems ranging from 2×8 ladders (32 Cu and 44 O sites; 76 total lattice sites) to 4×8 ladders (64 Cu and 88 O sites; 152 total lattice sites), with calculations extending to systems as large as 4×16 ladders. Simulations were performed over a range of hole dopings and charge-transfer energies, and the resulting bond orders and charge densities were calculated and compared. Comparison with Density Matrix Renormalization Group (DMRG) benchmark calculations demonstrated excellent agreement, validating the accuracy of CPQMC. For the larger ladder systems, the calculated bond orders and charge densities remained in good agreement with both our 2×8 CPQMC results and previously published DMRG calculations. These results demonstrate that CPQMC provides an accurate and computationally efficient framework for investigating larger coupled-ladder systems and enables the study of enhanced inter-ladder coupling and the emergence of two-dimensional electronic behavior in ladder cuprates.
