Promising ferroelectric metal EuAuBi with switchable giant shift current

The coexistence of metallicity and ferroelectricity in ferroelectric (FE) metals defies conventional wisdom and enables novel functionalities in electronic and optoelectronic systems. However, intrinsic FE metals remain extremely rare and challenging. Here, using first-principles calculations, we identify that a huge spontaneous polarization of 16.6-20.2 $μ\text{C}/\text{cm}^2$, a moderate switching barrier of 68.5 meV/f.u., and a low carrier concentration of $ \sim 2.5 \times 10^{20}$ cm$^{-3}$ coexist in topological semimetal EuAuBi. Further electron-phonon coupling calculations reveal that the metallic carriers interact weakly with the FE phonon mode, consistent with the decoupled electron mechanism. Moreover, EuAuBi exhibits a pronounced bulk photovoltaic effect characterized by a giant polarization-dependent shift current with the magnitude of conductivity up to 370 $μ\text{A}/\text{V}^2$. Thus, a feasible FE metal verification setup is proposed based on the shift current measurement. These results not only demonstrate that EuAuBi is a promising FE metal, but also propose a practical route for FE metals identification, which could promote the FE metals study greatly.