Tunable Quantum Layer Spin Hall Effect in Bilayer Altermagnetic Nb2SeTeO

Two-dimensional altermagnets have recently gained attention for enabling spin-polarized transport without net mag netization. The van der Waals layered form introduces an additional layer degree of freedom, allowing new ways to control spin and valley behaviors through interlayer coupling and external modulation. In our work, bilayer Nb2SeTeO shows tunable magnetic and topological properties based on first-principles calculations. The stacking configuration strongly influences its electronic structure and spin-valley characteristics. External electric fields and strain effectively modulate these properties. Compressive biaxial strain drives a transition to a quantum spin Hall phase with a high spin Chern number, while compressive uniaxial strain induces a quantum layer spin Hall effect, where layer-coupled chiral edge states can be switched by applying uniaxial strain in two vertical directions. These results identify bilayer Nb2SeTeO as a promising material for spintronic devices with controllable topological phases.