This talk was part of the Workshop on "Spin-Orbit Entangled Quantum Magnetism" held at the ESI September 23 -- 27, 2024.

Francesco Foggetti (IIT Genova, Uppsala Univ.), Louis Ponet (IIT Genova, EPFL), Daniel Khomskii (Univ. of Cologne)

IrTe2 is a layered transition metal dichalcogenide with anions and cations among the champions in spin orbit coupling strength. Below 280 K, IrTe2 manifests a sequence of states where some Ir-Ir bonds shorten by almost 20%, thus forming dimers, which order in stripes, interspaced by several undimerized rows. Here we aim to rationalize such ordering using a minimal model, with the choice of model parameters guided by first principles calculations.

We find that the total energy is decreasing approximately linearly with the dimer fraction for the previously observed phases, with the minimum for period-6 state. Dimer formation shifts the phonon density of states to higher frequencies, into the dimer-localized phonon bands. We describe the interactions between dimers using the force constant matrix from ab-initio calculations, and find features, similar to those driving striped orders in orthorhombic manganites. The strain texture is consistent with the observed striped orders. A simplified model, based on dimer energetics and phonon entropy, suggests a phase diagram of IrTe2 with a sequence of striped phases.