Two-Dimensional Altermagnetism in Epitaxial CrSb Ultrathin Films

Abstract

Altermagnets constitute an emerging class of collinear magnets that exhibit zero net magnetization yet host spin-split electronic bands arising from non-relativistic spin-space-group symmetries. Realization of altermagnetism in the two-dimensional (2D) limit remains an outstanding challenge because dimensional reduction suppresses kZ dispersion and destabilizes the symmetry operations essential for spin compensation. Here, we investigate ultrathin CrSb films grown epitaxially on Bi2Te3 substrate and uncover the evolution of altermagnetism in the 2D limit. Scanning tunneling microscopy (STM), quasiparticle interference (QPI), angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) calculations show that interfacial symmetry breaking in the one-unit-cell (1 UC) limit gives rise to localized electronic states and uncompensated magnetic moments. These interfacial effects become weakened from 7/4 UC, accompanied by the recovery of a bulk-like coordination environment and the emergence of altermagnetic electronic characteristics. Our results show that the essential altermagnetic electronic structure of CrSb survives at a thickness of only ~1.05 nm, demonstrating the robustness of altermagnetism in the 2D limit and opening opportunities for integrating stray-field-free spin order into low dimensional spintronic architectures.