Strongly frustrated triangular spin lattice emerging from triplet dimer formation in honeycomb Li2IrO3.

Satoshi Nishimoto,Viktor Yushankhai,Hermann Stoll,Liviu Hozoi,Ulrich K Rößler,Vamshi M Katukuri,Ioannis Rousochatzakis,Jeroen Van Den Brink

doi:10.1038/ncomms10273

Abstract

Iridium oxides with a honeycomb lattice have been identified as platforms for the much anticipated Kitaev topological spin liquid: the spin-orbit entangled states of Ir4+ in principle generate precisely the required type of anisotropic exchange. However, other magnetic couplings can drive the system away from the spin-liquid phase. With this in mind, here we disentangle the different magnetic interactions in Li2IrO3, a honeycomb iridate with two crystallographically inequivalent sets of adjacent Ir sites. Our ab initio many-body calculations show that, while both Heisenberg and Kitaev nearest-neighbour couplings are present, on one set of Ir–Ir bonds the former dominates, resulting in the formation of spin-triplet dimers. The triplet dimers frame a strongly frustrated triangular lattice and by exact cluster diagonalization we show that they remain protected in a wide region of the phase diagram.

Highlights

Iridium oxides with a honeycomb lattice have been identified as platforms for the much anticipated Kitaev topological spin liquid: the spin-orbit entangled states of Ir4 þ in principle generate precisely the required type of anisotropic exchange
As early as in the 1970s it was suggested that quantum spins in a solid can, instead of ordering in a certain pattern, form a fluid type of ground state—a quantum spin liquid[1,2]
As for the hole the latter is lowest in energy, an effective spin J 1⁄4 1=2 doublet defines to first approximation the local ground state of the Ir4 þ ion

Summary

Introduction

Iridium oxides with a honeycomb lattice have been identified as platforms for the much anticipated Kitaev topological spin liquid: the spin-orbit entangled states of Ir4 þ in principle generate precisely the required type of anisotropic exchange. In the honeycomb lattice Kitaev spin model[4], for instance, a spin-liquid state that has different topological phases with elementary excitations displaying Majorana statistics has been anticipated. This has been argued to be relevant for applications in topological quantum computing[5,6,7,8,9]. Finding materials in which the Kitaev spin model and the spin-liquid ground state are realized has proven to be very challenging[3] In this respect the strongly spin-orbit coupled honeycomb iridates have recently been brought to the fore[10,11]. As for the hole the latter is lowest in energy, an effective spin J 1⁄4 1=2 doublet (often referred to as a pseudospin ~S) defines to first approximation the local ground state of the Ir4 þ ion

Methods

Results

Conclusion