Circulating-current states and ring-exchange interactions in cuprates

TL;DR

This paper investigates how ring-exchange interactions influence circulating-current states in cuprates, using Hartree-Fock and Gutzwiller methods to analyze charge and spin flux phases in a Hubbard model.

Contribution

It introduces the impact of ring-exchange interactions on current phases in cuprates and compares Hartree-Fock results with Gutzwiller-projected states to assess correlation effects.

Findings

Charge flux states may be competitive in cuprates.

Spin flux states are suppressed in strongly correlated regimes.

Ring-exchange interactions significantly affect current-carrying states.

Abstract

We consider the consequences for circulating-current states of a cyclic, four-spin, ``ring-exchange'' interaction of the type shown recently to be significant in cuprate systems. The real-space Hartree-Fock approach is used to establish the existence of charge-current and spin-current phases in a generalized Hubbard model for the CuO_2 planes in cuprates. We compare the results of the Hartree-Fock approximation with the correlated states renormalized by Gutzwiller projection factors which allows us to gauge the qualitative effects of projection to no double site occupancy. We find that charge flux states may be competitive in cuprates, whereas spin flux states are suppressed in the strongly correlated regime. We then include the ring-exchange interaction and demonstrate its effect on current-carrying states both at and away from half-filling.