One- and Two-Particle Correlation Functions in the Cluster Perturbation Theory for Cuprates

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Strong electronic correlations in high-Tc superconducting cuprates complicate understanding their physics.
• Cluster perturbation theory (CPT) offers a method to approximate solutions for complex correlated systems.
• Accurate modeling of cuprate behavior requires accounting for both spin and charge dynamics.

Purpose of the Study:

• To develop and apply cluster perturbation theory (CPT) for dynamic spin and charge susceptibilities in cuprates.
• To investigate the doping dependence of spin susceptibility in high-Tc superconductors.
• To compare theoretical predictions with experimental results from inelastic neutron scattering.

Main Methods:

• Developed spin-CPT and charge-CPT, incorporating exact diagonalization for electronic correlations.
• Applied developed methods to the two-band Hubbard model derived from the Emery model for cuprates.
• Calculated one- and two-particle correlation functions, including spectral functions and susceptibilities.

Main Results:

• In the underdoped region, spin-CPT and CPT-RPA predict an upper spin excitation branch with minimum energy at (π,π).
• No low-energy incommensurate excitations were found in the underdoped region by either method.
• In the overdoped region, both methods show a low-energy response at four incommensurate wave vectors, aligning with experiments.

Conclusions:

• The developed spin-CPT and charge-CPT methods accurately capture essential physics of high-Tc cuprates.
• Theoretical predictions for spin excitation dispersion and incommensurate responses are validated by experimental data.
• CPT provides a robust framework for studying strongly correlated electron systems like superconducting cuprates.