Stoichiometric Control of Intrinsic Magnetic Weyl Semimetallic State in SrRuO ₃ (111) Ultra‐Thin Films

Precise control over stoichiometry is essential for stabilizing exotic electronic phases in complex oxide thin films. Realizing the intrinsic magnetic Weyl semimetal (MWSM) phase in ultra‐thin (SRO) films poses a substantial experimental challenge due to difficulties in controlling Ru stoichiometry. Here, we leverage pulsed laser deposition to stabilize the intrinsic MWSM phase in SRO films down to 4 nm. Optimized growth conditions yield near‐stoichiometric, high‐quality films exhibiting a Curie temperature K and a large residual resistivity ratio ( RRR ). By tuning the Ru content, we observe a transition from the MWSM to a conventional magnetic semimetal. The MWSM phase is evidenced in films as thin as 4 nm by key signatures: large, non‐saturating positive magnetoresistance (95% in 18 nm and 30.6% in 4 nm films at 2 K) and Shubnikov–de Haas oscillations. Analysis of these oscillations reveals high‐mobility Weyl fermions ( ) with small effective masses of and for the 4 nm and 18 nm films, respectively. Density functional theory corroborates these findings, showing Weyl nodes near the Fermi level with similar effective masses (0.12). Altogether, our work demonstrates the stoichiometry‐controlled realization of the intrinsic MWSM state in nanoscale SRO.