Nonsymmorphic Symmetry Induced Correlated Topological States in 4D Perovskite Oxide Thin Films

Quantum materials (QMs) with strong correlation and nontrivial topology are indispensable to next-generation information and computing technologies and microelectronics. Exploiting topological band structure is an ideal starting point to realize correlated topological QMs. Despite its potential, observation of such topological band structure to enable quantum transport in oxide materials remains challenging. Our recent findings indicate that manipulating oxygen octahedral symmetry (OOS) is one of the key approaches in creating topological band structures near the Fermi level. In this work, we synthesize 4<i>d</i> niobate thin films (e.g., SrNbO₃ and CaNbO₃) and manipulate crystal symmetry by epitaxial strain to induce the nonsymmorphic crystal symmetry, yielding the topological band structure and related physical properties. The 4<i>d</i> niobate thin films exhibited extremely high electron mobility and non-saturated extreme magnetoresistance due to the linear band dispersion near the Fermi level. Moreover, quantum oscillation from the magnetotransport measurements and the corresponding Landau-Fan diagram confirm a non-zero Berry phase. Therefore, the deliberate control of the octahedral symmetry provides a novel mechanism to host topological band structures in the strongly correlated oxide systems, which is an important step toward developing correlated topological quantum materials.