Ferroelectric order versus metallicity in Sr${}_{1-x}$Ca${}_x$TiO${}_{3-\delta }$ ($x=0.009$)

Abstract

We report on a thermal-expansion study of the ferroelectric phase transition in insulating Sr${}_{1-x}$Ca${}_x$TiO${}_3$ ($x=0.009$) and its evolution upon increasing charge-carrier concentration up to $n\simeq 60\times 10^{19}$cm${}^{-3}$. Although electric polarization is screened by mobile charge carriers, we find clear signatures of the ferroelectric phase transition in the thermal-expansion coefficient $\alpha$ of the weakly doped metallic samples. Upon increasing $n$, the transition temperature $T_{\mathrm{C}}(n)$ and the magnitude of the anomalies in $\alpha$ rapidly decrease up to a threshold carrier density $n^{\star }$ above which broadened anomalies remain present. There is no indication for a sign change of $\alpha$ as is expected for a pressure-dependent quantum phase transition with $n$ as the control parameter. Thus, the ferroelectriclike transition is either continuously fading away or it transforms to another low-temperature phase above $n^{\star }$, but this change hardly affects the temperature-dependent $\alpha (T)$ data.

arXiv comment6 pages, 3 figures

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• Spin-Phonon Resonances in Nearly Polar Metals with Spin-Orbit Coupling
• Majorana-Weyl cones in ferroelectric superconductors
• Mechanism for Switchability in Electron-Doped Ferroelectric Interfaces
• Modeling polar order in compressively strained SrTiO${}_3$