Strain-Driven Higher-Order Topological Dirac Semimetal in Noncentrosymmetric γ-GeSe

Strain-engineered topological phases in noncentrosymmetric materials offer fertile ground for realizing exotic quantum states, yet their experimental realization remains elusive. Here, using first-principles calculations, we demonstrate that the van der Waals layered material γ-GeSe undergoes a sequence of strain-induced topological phase transitions, including the emergence of a higher-order topological Dirac semimetal phase. Under in-plane biaxial tensile strain, we uncover a sequential evolution of topological phases, including topological nodal-line semimetals, Dirac semimetals, and a higher-order topological Dirac semimetal phase. Notably, the noncentrosymmetric higher-order topological Dirac semimetal phase is characterized by Dirac points coexisting with higher-order topological insulating phases on the k_z = 0 plane, enabled by quantization of the mirror-resolved Zak phase. These findings position γ-GeSe as an experimentally viable platform for investigating strain-engineered topological phenomena unique to noncentrosymmetric systems.