Extreme tensile strain states in magnetic oxide membranes*

A defining feature of emergent phenomena in complex oxides is the competition and cooperation between ground states. In manganites the balance between metallic and insulating phases can be tuned by the lattice[1]; extending the range of lattice control would enhance the ability to access other phases. Freestanding complex oxide membranes[2] provide unique opportunities to realize previously unobserved strain-induced responses. Oxide membranes can be mechanically coupled to an external platform without an epitaxial relationship, of which strain states and symmetries can be freely chosen by design. Moreover, the critical fracture strain is often greatly enhanced for small materials length scales, allowing tensile strain states larger than the typical values ceramics withstand. Here we stabilize uniform tensile strain in La_0.7Ca_0.3MnO₃ membranes, exceeding 8% uniaxially and 5% biaxially[3]. Uniaxial and biaxial strain suppresses the ferromagnetic metal at distinctly different strain values, inducing an insulator that can be extinguished by magnetic field. This highly-tunable strained membrane approach provides a broad opportunity to design and manipulate correlated electron states.

[1] Y. Tokura, Reports on Progress in Physics 69, 797 (2006).
[2] D. Lu et al., Nature Materials 15, 1255 (2016)
[3] S.S. Hong et al., Science 368, 71 (2020)