The fate of electric dipoles inside a Fermi sea is an old issue, yet poorly explored. Sr\({}_{1-x}\)Ca\({}_{x}\)TiO\({}_{3}\) hosts a robust but dilute ferroelectricity in a narrow (\(0.0018\ <\ x\ <\ 0.02\)) window of substitution. This insulator becomes metallic by removal of a tiny fraction of its oxygen atoms. Here, we present a detailed study of low-temperature charge transport in Sr\({}_{1-x}\)Ca\({}_{x}\)TiO\({}_{3-\delta }\), documenting the evolution of resistivity with increasing carrier concentration (\(n\)). Below a threshold carrier concentration, \({n}^{* }(x)\), the polar structural-phase transition has a clear signature in resistivity and Ca substitution significantly reduces the 2 K mobility at a given carrier density. For three different Ca concentrations, we find that the phase transition fades away when one mobile electron is introduced for about \(7.9\pm 0.6\) dipoles. This threshold corresponds to the expected peak in anti-ferroelectric coupling mediated by a diplolar counterpart of Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction. Our results imply that the transition is driven by dipole–dipole interaction, even in presence of a dilute Fermi sea. Charge transport for \(n\ <\ {n}^{* }(x)\) shows a non-monotonic temperature dependence, most probably caused by scattering off the transverse optical phonon mode. A quantitative explanation of charge transport in this polar metal remains a challenge to theory. For \(n\ge {n}^{* }(x)\), resistivity follows a T-square behavior together with slight upturns (in both Ca-free and Ca-substituted samples). The latter are reminiscent of Kondo effect and most probably due to oxygen vacancies.

费米海中电偶极子的命运是一个古老的问题，但尚未得到很好的探索。Sr \ {{} _ {1-x} \） Ca \ {{} _ {x} \） TiO \ {{} _ {3} \）在狭窄的地方（\（0.0018 \ < \ x \ <\ 0.02 \））替换窗口。通过除去极少量的氧原子，该绝缘体就变成金属。在这里，我们对Sr \（{} _ {1-x} \） Ca \ {{} _ {x} \） TiO \ {{} _ {3- \ delta}中的低温电荷传输进行了详细的研究。\），记录了电阻率随载流子浓度（\（n \））的增加而变化的过程。低于阈值载流子浓度\（{n} ^ {*}（x）\），极性结构相变在电阻率上具有明显的特征，并且在给定的载流子密度下，Ca取代会显着降低2 K迁移率。对于三种不同的Ca浓度，我们发现，当一个移动电子被引入约\（7.9 \ pm 0.6 \） 偶极子时，相变逐渐消失。该阈值对应于Ruderman–Kittel–Kasuya–Yosida（RKKY）相互作用的双偶极体介导的反铁电耦合的预期峰值。我们的结果表明，即使存在稀薄的费米海，过渡也是由偶极-偶极相互作用驱动的。\（n \ <\ {n} ^ {*}（x）\）的电荷传输显示出非单调的温度依赖性，这很可能是由横向光学声子模式的散射引起的。对这种极性金属中电荷传输的定量解释仍然是理论上的挑战。对于\（n \ ge {n} ^ {*}（x）\），电阻率遵循T平方行为，并伴有轻微上浮（在无Ca和Ca取代的样品中）。后者使人联想到近藤效应，很可能是由于氧空位引起的。