Intrinsic ferroelastic valleytronics in 2D Pd₄X₃Te₃ (X = S, Se) materials: a new platform for ultrafast intervalley carrier dynamics

Realizing and manipulating valley polarization remains a significant challenge in the field of valleytronics. The prevailing paradigm in this area primarily focuses on valleys associated with ferromagnetic and ferroelectric properties. In this study, we go beyond the existing paradigm to propose a novel mechanism, termed ferroelastic valleytronics. The inversion of the valley index is achieved through transformations of the ferroelastic state. Using first-principles calculations and model analysis, we validate this concept in Pd₄X₃Te₃, a material with intrinsic valley polarization that is ferroelastically controllable. Beyond its intrinsic valley polarization and ferroelasticity, Pd₄X₃Te₃ exhibits a range of intriguing physical phenomena, including anisotropic carrier mobility at valleys, ferroelastic-correlated Hall coefficients, and valley-contrasted selectivity for linearly polarized light. Furthermore, non-adiabatic molecular dynamics (NAMD) simulations reveal the dynamics of intervalley carrier transfer and recombination in Pd₄X₃Te₃. Our results indicate that hole transfer between valleys occurs more rapidly than electron transfer and that intervalley carrier recombination takes place on the nanosecond timescale. This theoretical research not only provides a promising approach to control valley polarization but also advances the emerging field of valleytronics.