Revealing frustrated local moment model for pressurized hyperhoneycomb iridate: Paving the way toward a quantum spin liquid

Abstract

There have been tremendous experimental and theoretical efforts toward discovery of quantum spin liquid phase in honeycomb-based-lattice materials with strong spin-orbit coupling. Here the bond-dependent Kitaev interaction between local moments provides strong magnetic frustration and if it is the only interaction present in the system, it will lead to an exactly solvable quantum spin liquid ground state. In all of these materials, however, the ground state is in a magnetically ordered phase due to additional interactions between local moments. Recently, it has been reported that the magnetic order in hyperhoneycomb material, $\beta$-Li$_2$IrO$_3$, is suppressed upon applying hydrostatic pressure and the resulting state becomes a quantum paramagnet or possibly a quantum spin liquid. Using ab-initio computations and strong coupling expansion, we investigate the lattice structure and resulting local moment model in pressurized $\beta$-Li$_2$IrO$_3$. Remarkably, the dominant interaction under high pressure is not the Kitaev interaction nor further neighbor interactions, but a different kind of bond-dependent interaction. This leads to strong magnetic frustration and may provide a platform for discovery of a new kind of quantum spin liquid ground state.