Ferroelectric enhancement of superconductivity in compressively strained SrTiO3 films
Ferroelectric enhancement of superconductivity in compressively strained SrTiO3 films
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DOI：
10.1103/physrevmaterials.3.091401
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发表时间：
2019-09-06
影响因子：
3.4
通讯作者：
Harter, John W.
中科院分区：
文献类型：
--
作者：
Russell, Ryan;Ratcliff, Noah;Harter, John W.
SrTiO 3是一种处于极性不稳定性边缘的初期铁电体，在低温下通过量子涨落避免了极性不稳定性。在这个不寻常的量子顺电相内，尽管载流子密度极其稀薄，超导电性仍然存在。铁电涨落被怀疑通过促进电子配对在超导电性的起源中起作用。为了研究这种可能性，我们使用光学二次谐波产生来测量压应变SrTiO 3薄膜中的铁电序参数的掺杂和温度依赖性。在低温下，我们发现了一个自发的平面外的铁电极化与正常状态的电阻率异常的发病完全相关。这些异常先前已与掺杂SrTiO 3膜中的超导临界温度的增强相关联，直接连接铁电相和超导相。我们开发了一个长程平均场伊辛模型的铁电相变解释的数据，并提取系统中的相关能量尺度。我们的研究结果支持长期怀疑SrTiO 3的铁电性和超导性之间的联系，但质疑铁电波动所发挥的作用。
SrTiO3 is an incipient ferroelectric on the verge of a polar instability, which is avoided at low temperatures by quantum fluctuations. Within this unusual quantum paraelectric phase, superconductivity persists despite extremely dilute carrier densities. Ferroelectric fluctuations have been suspected to play a role in the origin of superconductivity by contributing to electron pairing. To investigate this possibility, we used optical second harmonic generation to measure the doping and temperature dependence of the ferroelectric order parameter in compressively strained SrTiO3 thin films. At low temperatures, we uncover a spontaneous out-of-plane ferroelectric polarization with an onset that correlates perfectly with normal-state electrical resistivity anomalies. These anomalies have previously been associated with an enhancement of the superconducting critical temperature in doped SrTiO3 films, directly linking the ferroelectric and superconducting phases. We develop a long-range mean-field Ising model of the ferroelectric phase transition to interpret the data and extract the relevant energy scales in the system. Our results support a long-suspected connection between ferroelectricity and superconductivity in SrTiO3, but call into question the role played by ferroelectric fluctuations.