Strain-engineered interaction of quantum polar and superconducting phases*

Much of the focus of modern condensed matter physics concerns control of quantum phases with examples that include flat band superconductivity in graphene bilayers, the interplay of magnetism and ferroelectricity, and induction of topological transitions by strain. Here we report the first observation of a reproducible and strong enhancement of the superconducting critical temperature, T_c, in strontium titanate (SrTiO₃) obtained through careful strain engineering of interacting superconducting phase and the polar quantum phase (quantum paraelectric). Our results show a nearly 50% increase in T_c with indications that the increase could become several hundred percent. We have thus discovered a means to control the interaction of two quantum phases through application of strain, which may be important for quantum information science. Further, our work elucidates the enigmatic pseudogap-like and preformed electron pairs phenomena in low dimensional strontium titanate as potentially resulting from the local strain of jammed tetragonal domains.