Strain Tuning of Weyl Nodes in SrRuO ₃ Membranes

Free-standing membranes are an exciting recent development in the field of complex oxides, allowing intrinsic material properties and phenomena to be probed in ways that would be difficult or otherwise inaccessible in epitaxially bound heterostructures. By employment of a water-soluble sacrificial layer of Sr₃Al₂O₆, strain-free ultrathin SrRuO₃ membranes have been fabricated that exhibit bulk lattice parameters and ferromagnetism at a Curie temperature of 150 K with the magnetic easy axis oriented 22° off the normal. The presence of sizable negative longitudinal magnetoresistance provides a direct signature of the decisive role played by Weyl Fermions in magnetotransport. In addition, a sign change between the strained films and free-standing SrRuO₃ membranes of in-plane transversal magnetotransport indicates a strong electromechanical coupling, resulting in a change of the Fermi velocity of Weyl Fermions. Our measurements provide a first insight into the magnetoelectric properties of SrRuO₃ membranes, highlighting the influence of the exfoliation process on structural, electronic, and magnetic degrees of freedom.