2025/09/13 by Ikaida, Riku, Sano, Kazuhiro, Masuda, Yoshimi +2
#FOS: Physical sciences #Superconductivity (cond-mat.supr-con)
paper · doi:10.48550/arxiv.2509.10881
Electron-doped strontium titanate \rmSrTiO3, known to be one of the most dilute superconductors, is investigated on the basis of the first-principles calculations. When the carrier density n decreases, the frequencies of the ferroelectric optical phonons near the Γ-point monotonically decreases in the overdoped regime with n<1020/\rmcm3, while unphysical imaginary phonon frequencies due to ferroelectric instabilities appear in the underdoped regime with n>1020/\rmcm3. We estimate the superconducting transition temperature T_\rmc by using the McMillan equation in the overdoped regime and find that T_\rmc increases with decreasing n as consistent with experiments in the overdoped regime. Detailed analysis of the Eliashberg function reveals that the increases in T_\rmc with decreasing n in the overdoped regime is mainly due to the contributions from the ferroelectric soft-mode optical phonons.