Classical spin liquid instability driven by off-diagonal exchange in strong spin-orbit magnets

TL;DR

This paper demonstrates that off-diagonal exchange anisotropy in strong spin-orbit Mott insulators induces a classical spin liquid state with extensive degeneracy, influencing magnetic order and explaining experimental observations in certain iridates.

Contribution

It reveals how off-diagonal exchange anisotropy drives classical spin liquid behavior in 2D and 3D spin-orbit coupled Mott insulators, providing a unified theoretical framework.

Findings

Off-diagonal exchange anisotropy induces classical spin liquid regimes.

Quantum fluctuations can either preserve degeneracy or select non-collinear states.

Results explain suppression of magnetic signals in $eta$-Li$_2$IrO$_3$ under pressure.

Abstract

We show that the off-diagonal exchange anisotropy drives Mott insulators with strong spin-orbit coupling to a classical spin liquid regime, characterized by an infinite number of ground states and Ising variables living on closed or open strings. Depending on the sign of the anisotropy, quantum fluctuations either fail to lift the degeneracy down to very low temperatures, or select non-collinear magnetic states with unconventional spin correlations. The results apply to all 2D and 3D tri-coordinated materials with bond-directional anisotropy, and provide a consistent interpretation of the suppression of the x-ray magnetic circular dichroism signal reported recently for $\beta$-Li$_2$IrO$_3$ under pressure.