Interplay between Ferrolectricity And Superconductivity

铁电性和超导性之间的相互作用

• 批准号: 407166196
• 负责人: Professor Dr. Joachim Hemberger
• 金额: --
• 依托单位: Institut für Experimentalphysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/407166196?language=en
• 关键词: Interplay; between; Ferrolectricity; Superconductivity

Among doped semiconductors with a superconducting ground state, SrTiO3 is distinguished by the precocity of its superconductivity. With only 10-5 electrons per formula unit(f.u.), the system becomes superconducting. When carrier density exceeds 0.02/f.u., it ceases to be so. This superconducting dome raises two distinct and still unanswered questions: how does superconductivity persist in the dilute limit despite the hierarchy inversion between Fermi and Debye temperatures? Why does it disappear on the overdoped side in spite of the steady increase in the electronic density of states? The insulating parent of this remarkable superconductor is a quantum paraelectric, which becomes a true ferroelectric by replacing strontium with calcium. The two partners have recently discovered that the two orders coexist in Ca-substituted-oxygen-deficient strontium titanate. At first sight, such a coexistence appears surprising. Ferroelectricity is a state of matter in which the solid hosts a macroscopic reversible static electric dipole. Since mobile electrons of a metal are expected to screen such a dipole, only ionic insulators which lack inversion symmetry are expected to qualify as true ferroelectrics. Superconductivity is an electron instability in a metal triggered by an attractive interaction overcoming the Coulomb repulsion among electrons and creating Cooper pairs which condensate macroscopically. These two states of matter have little in common. Their mutual exclusiveness was considered even stronger than the documented animosity between superconductivity and magnetism. However, we have found that when mobile electrons and electric dipoles are both dilute, they can coexist and the superconducting instability of electrons and ferroelectric alignment of dipoles do not impede each other. This experimental observation raises a host of new questions: How many mobile electrons does it take to screen a dipole and how do the dynamical aspects of the screening process have to be considered in the dilute limit? How do dipoles inside a Fermi sea communicate with each other? How do Cooper pairs and aligned dipoles interact? How to compare ferroelectric quantum criticality with its magnetic counterpart?This proposal aims to document the consequences of the proximity between ferroelectric, superconducting and antiferrodistortive orders in SrTiO3 subject to various dopants (niobium, lanthanum, calcium, barium, oxygen vacancies…) as well as in its sister compound EuTiO3. The two partners possess complementary expertise. The German partner has been active in exploring the complex conductance in a broad range of frequency and has strong expertise in single-crystal growth of rare-earth titanates and thermodynamic studies of quantum phase transitions. The French partner has been studying electric, thermoelectric and thermal transport at zero frequency in extreme conditions of temperature and magnetic field.

在具有超导基态的掺杂半导体中，SrTiO 3以其超导电性的早熟而闻名。每个分子式单位（f.u.）只有10-5个电子，系统变成超导体。当载流子密度超过0.02/f.u.时，就不再是这样了。这个超导圆顶提出了两个截然不同的问题，但仍然没有答案：尽管费米温度和德拜温度之间存在层次倒置，超导性如何在稀释极限中持续存在？为什么它在过掺杂的一侧消失，尽管电子态密度稳定增加？这种非凡超导体的绝缘母体是量子顺电体，它通过用钙取代锶而成为真正的铁电体。 这两个合作伙伴最近发现，这两个订单共存于钙取代的缺氧钛酸锶。乍一看，这种共存似乎令人惊讶。铁电性是一种物质状态，其中固体拥有宏观可逆的静电偶极子。由于金属的移动的电子被期望屏蔽这样的偶极子，因此只有缺乏反转对称性的离子绝缘体被期望有资格成为真正的铁电体。超导是金属中的电子不稳定性，其由吸引相互作用触发，克服电子之间的库仑排斥并产生宏观上冷凝的库珀对。这两种物质状态几乎没有共同之处。它们的相互排斥性被认为比超导性和磁性之间的记录敌意更强。然而，我们发现当移动的电子和电偶极子都是稀的时，它们可以共存，并且电子的超导不稳定性和电偶极子的铁电排列并不相互阻碍。这一实验观察提出了一系列新的问题：屏蔽一个偶极子需要多少移动的电子？在稀释极限下，屏蔽过程的动力学方面必须如何考虑？费米海中的偶极子是如何相互联系的？库珀对和排列的偶极子如何相互作用？如何比较铁电量子临界性与磁性量子临界性？该提案旨在记录SrTiO 3中的铁电，超导和反铁畸变订单之间的接近的后果，受到各种掺杂剂（铌，镧，钙，钡，氧空位.）以及其姊妹化合物EuTiO 3。这两个伙伴拥有互补的专门知识。德国合作伙伴一直积极探索在广泛的频率范围内的复杂电导，并在稀土钛酸盐的单晶生长和量子相变的热力学研究方面拥有丰富的专业知识。法国合作伙伴一直在研究极端温度和磁场条件下零频率下的电，热电和热传输。