Colossal photovoltages in strain-driven crystal field transition and symmetry breaking of superconducting epitaxial systems

Abstract

Materials showing light-induced voltages (LIVs) are a flourishing class characterized by anisotropic charge transport. The LIVs' functionality could be tuned by local perturbations and structural symmetry, but achieving large LIVs is still challenging and a clear guiding principle to this end thus remains to be established. Here, a long-range lattice strain approach that enables manipulating the crystal field and symmetry breaking is proposed to realize colossal LIVs. The tailored tensile and compressive strains are introduced into superconducting $(\mathrm{L}{\mathrm{a}}_{1.45}\mathrm{N}{\mathrm{d}}_{0.4})\mathrm{S}{\mathrm{r}}_{0.15}\mathrm{Cu}{\mathrm{O}}_{4}$ epitaxial films that are fabricated by the pulsed laser deposition method. The experimental characterization indicates that long-range lattice compressive strain results in the epitaxially mosaic structures and the local crystal field transition from tetragonal to octahedral configurations that spontaneously breaks the symmetry. Such a structural transition and change through modulated compressive strain could greatly favor in-plane transport that contributes to a large anisotropy of the Seebeck coefficient $\mathrm{\ensuremath{\Delta}}S$ of over $100\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{V}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$, achieving strikingly colossal LIVs of over 70 V, many times larger than those of existing materials reported. This would broaden LIVs' promising application in light or photovoltage response and also exemplifies a steady route to exploring new high-performance LIV materials with structural or transport anisotropy.