Examining the surface phase diagram of IrTe${}_2$ with photoemission

Abstract

In the transition metal dichalcogenide IrTe${}_2$, low-temperature charge-ordered phase transitions involving Ir dimers lead to the occurrence of stripe phases of different periodicities, and nearly degenerate energies. Bulk-sensitive measurements have shown that, upon cooling, IrTe${}_2$ undergoes two such first-order transitions to $(5\times 1\times 5)$ and $(8\times 1\times 8)$ reconstructed phases at $T_{c_1}\sim 280$~K and $T_{c_2}\sim 180$~K, respectively. Here, using surface sensitive probes of the electronic structure of IrTe${}_2$, we reveal the first-order phase transition at $T_{c_3}=165$~K to the $(6\times 1)$ stripes phase, previously proposed to be the surface ground state. This is achieved by combining x-ray photoemission spectroscopy and angle-resolved photoemission spectroscopy, which give access to the evolution of stripe domains and a particular surface state, the energy of which is dependent on the Ir dimer length. By performing measurements over a full thermal cycle, we also report the complete hysteresis of all these phases.