Ruthenates with perovskite and perovskite-related structures host a remarkably diverse class of exotic quantum phases ranging from spin-triplet superconductivity, ferromagnetism, metamagnetism, spin-density waves, antiferromagnetism, and quantum criticality—all with the same basic building block of corner-sharing RuO6 octahedra containing Ru4+ ions. We exploit strain engineering1 to tune the band structure of the complex oxide ruthenates: CaRuO3,2,3 SrRuO3,3,4 and BaRuO3,5 with the perovskite structure as well as their two-dimensional counterparts Sr2RuO4 and Ba2RuO4.6 The ruthenate films are grown by reactive molecular-beam epitaxy (MBE) and the misfit strain is imposed by underlying substrates to strain these complex oxide thin films to percent levels3—far beyond where they would crack or plastically deform in bulk. The band structure is revealed by high-resolution angle-resolved photoemission (ARPES) on pristine as-grown surfaces of these complex oxides made possible by a direct ultra-high vacuum connection between the MBE and ARPES. Our work demonstrates the possibilities for utilizing strain engineering as a disorder-free means to manipulate emergent properties and many-body interactions in correlated materials.
