Controlling the charge ordering behaviour in IrTe2 with uniaxial strain

The interplay between multiple degrees of freedom in correlated systems is responsible for numerous emergent phases and the competition between nearly degenerate ground states. In recent decades, considerable effort has been made employing external perturbations to push materials away from their equilibrium configurations in order to access previously unexplored phases. Within this context, uniaxial strain has recently emerged as a powerful approach to influence emergent behaviour [1].

We present angle-resolved photoemission spectroscopy (ARPES) measurements combined with uniaxial strain on the transition metal dichalcogenide IrTe2. This high-atomic number material is predicted to be a type-II bulk Dirac semimetal, and presents multiple first-order bulk structural phase transitions involving a charge transfer from Ir 5d to Te 5p states. Previous work has suggested the transitions might be stabilized by a spin-orbit Mott mechanism [2]. A significant challenge in understanding this material is that a number of nearly degenerate structural phases coexist at the surface with a spatial variation of just a few tens of nanometres, making the momentum-resolved electronic structure in the charge ordered phases inaccessible.

By applying a modest uniaxial strain (~ 0.1%) to IrTe2 single crystals, we demonstrate the selective stabilization of a single structural phase with domain sizes four orders of magnitude larger than in unstrained samples [3]. We show that a strain induced charge transfer into Te anti-bonding states weakens the interlayer polymeric bonds and thereby lifts the phase degeneracy. This stabilisation allows unprecedented spectroscopic access to the ground state of IrTe2, including the previously unobserved Dirac dispersions. Due to the broken rotational symmetry in the charge ordered ground state, these bulk states undergo a topological phase transition and become gapped, leaving a protected surface Dirac cone and topologically non-trivial states at the Fermi level [4]. The strain-induced stabilization opens up the possibility to further study the interplay between charge order, topology and itinerant electrons in a strongly spin-orbit coupled material.

[1] Hicks, C. W., et al. Science 344, 283–285 (2014); Kim, H. H. et al. Science 362, 1040–1044 (2018); Riccò, S. et al. Nat. Commun. 9, 4535 (2018); Lin, C. et al., Nat. Mat. 20, 1093 (2021)
[2] Ko, K.-T., et al., Nat. Commun, 6, 7342, (2015)
[3] Nicholson, C.W., et al. Commun. Mater. 2, 25 (2021); https://doi.org/10.1038/s43246-021-00130-5
[4] Nicholson, C.W., et al. in preparation