A Magnetic Model of the Tetragonal-Orthorhombic Transition in the Cuprates

TL;DR

The paper presents a magnetic model explaining the tetragonal-orthorhombic transition in cuprates, showing how layered frustrated antiferromagnets exhibit two phase transitions similar to those observed in certain cuprate materials.

Contribution

It introduces a quasi-2D Heisenberg antiferromagnet model with frustrated interlayer couplings that captures the sequence of structural and magnetic phase transitions in cuprates.

Findings

The model predicts two thermal phase transitions with symmetry breaking.

The temperature difference between transitions is smaller in the model than in La2CuO4.

The model may explain nearly coincident transitions in La2CaCuO6.

Abstract

It is shown that a quasi two dimensional (layered) Heisenberg antiferromagnet with fully frustrated interplane couplings ({\it e.g.} on a body-centered tetragonal lattice) generically exhibits two thermal phase transitions with lowering temperature -- an upper transition at $T_{TO}$ (``order from disorder without order'') in which the lattice point-group symmetry is spontaneously broken, and a lower N\'{e}el transition at $T_{N}$ at which spin-rotation symmetry is broken. Although this is the same sequence of transitions observed in La$_2$CuO$_4$, in the Heisenberg model (without additional lattice degrees of freedom) $(T_{TO}-T_N) /T_N$ is much smaller than is observed. The model may apply to the bilayer cuprate La$_2$CaCuO$_6$, in which the transitions are nearly coincident.