Uniaxial strain-induced phase transition in the 2D topological semimetal IrTe2

Abstract

Strain is ubiquitous in solid-state materials, but despite its fundamental importance and technological relevance, leveraging externally applied strain to gain control over material properties is still in its infancy. In particular, strain control over the diverse phase transitions and topological states in two-dimensional transition metal dichalcogenides remains an open challenge. Here, we exploit uniaxial strain to stabilize the long-debated structural ground state of the 2D topological semimetal IrTe2, which is hidden in unstrained samples. Combined angle-resolved photoemission spectroscopy and scanning tunneling microscopy data reveal the strain-stabilized phase has a 6 × 1 periodicity and undergoes a Lifshitz transition, granting unprecedented spectroscopic access to previously inaccessible type-II topological Dirac states that dominate the modified inter-layer hopping. Supported by density functional theory calculations, we show that strain induces an Ir to Te charge transfer resulting in strongly weakened inter-layer Te bonds and a reshaped energetic landscape favoring the 6×1 phase. Our results highlight the potential to exploit strain-engineered properties in layered materials, particularly in the context of tuning inter-layer behavior.

Local mechanism of valence bond formation in IrTe$_2$

“…Secondly, inverted band gaps of the bulk electronic structure are obtained as well. These inverted band gaps are expected to result in topological surface states and resonances 9 , which indeed appears to be consistent with a very recent ARPES-study 10 .…”

“…Fig. 1 (a,b)) IrTe 2 exhibits bulk Dirac points, spin-orbit driven gap inver-sions and the corresponding topological surface states, which all emerge from the Te 5p derived bands [9][10][11][12] . It is particularly exciting that this system not only hosts a topological electronic band structure but also superconductivity below 3 K, raising great hopes for intrinsic topological superconductivity [13][14][15][16] .…”

Break of symmetry at the surface of IrTe$_2$ upon phase transition measured by X-ray photoelectron diffraction

“…In the (5×1) phase, 5 atoms split in 2 dimerized Ir atoms represented with light blue bullets (one dimer) and 3 undimerized atoms [Figure 3 (a) & Figure 1 (cd)]. This leads to a splitting of the Ir 4f 7/2 core level into a contribution due to the dimerized Ir atoms [6,32,14,27], at higher binding energy, and a contribution due to the 3 undimerized Ir atoms. These different contributions in XPS are used to acquire XPD diffractograms specific to the local environment of the monomer (undimerised) and dimer Ir atoms.…”

“…A second phase transition occurs at T c 2 = 180 K, characterized by a bulk (8 × 1 × 8) superstructure. This has stimulated numerous scanning tunneling microscopy (STM) [22,15,6,18,23] and angle-resolved photoemission spectroscopy (ARPES) studies [14,24,25,26,6,27], which revealed additional periodicities and a surface periodicity (6 × 1) appearing after a third phase transition at T c 3 = 165 K. These surface-sensitive probes disclosed a complex evolution of the electronic structure of IrTe 2 through its phase transitions that calls for state-of-the-art ab-initio calculations for a better understanding. This requires the determination of the atomic structure of IrTe 2 in the different reconstructed phases up to a few atomic layers below the surface, to be comparable to the probing depth of typical ARPES measurements.…”

Spatially-resolved electronic structure of stripe domains in IrTe$_2$ through electronic structure microscopy

“…1b) to triclinic structure (P 1) around 280 K, accompanied by complex stripe phase 20 with periods of (3n+2)×1×(3n+2) (n = 1,2,3,...) in the bulk 20,21 and (3n+2)×1 on the surface 22,23 . Recent scanning tunnelling microscopy and ARPES study on strained IrTe 2 shows 6×1 phase can be stabilized by strain 24 . Suppressing the stripe phase by doping or intercalation 20,25 leads to emergence of superconductivity.…”