Ever since ferroelectric materials were first discovered, scientists have sought to understand how their properties relate to superconductivity. A recently discovered curiosity, for instance, is that these materials exhibit a puzzling “dome” in their critical superconducting temperature near their ferroelectric transitions. Now, Chandan Setty at Rice University, Texas, and colleagues provide a surprisingly simple explanation for this puzzle that uses lattice dynamics and phonons [1].
The superconducting dome is puzzling because of what the ferroelectric transition does to a material’s phonons. According to Bardeen-Cooper-Schrieffer (BCS) theory, phonons mediate the binding of electrons into superconductivity-producing Cooper pairs. But as a material nears the ferroelectric transition—as a result of doping or the application of strain, for example—these phonons are damped and have their lifetimes reduced. In a conventional superconductor, such phonon damping lowers the critical superconducting temperature; in a ferroelectric material, the critical temperature instead rises to a peak at the ferroelectric “instability point,” where the damping is greatest.
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