Phase Stabilization of Strained 1T Monolayer IrTe₂ by Electron-Phonon Coupling Modulation

Two-dimensional 1T monolayer (ML) IrTe₂ exhibits complex structural phase transitions in response to external stimuli such as temperature and strain. While various mechanisms have been proposed to explain rich structural phases, their origin remains unclear. In this study, we investigate the strain-induced phase transition in ML IrTe₂ using first-principles calculations and constrained density-functional perturbation theory. We find that biaxial tensile strain hardens the soft phonon modes associated with structural instability, stabilizing the trigonal phase. The strain, however, does not remove the sharp peaks in the electronic susceptibility from the Fermi surface nesting. We show that the renormalization of the phonon self-energy is primarily influenced by the interaction of phonons with electrons in low-energy bands crossing the Fermi level. Furthermore, we find that the off-diagonal matrix elements of the phonon self-energy are sensitive to biaxial tensile strain, which contributes to the stabilization of the soft phonon modes.