Materials World Network: Properties of Electrostatically Doped Oxide Superconductors

技术概述：本材料世界网络项目将通过实验合成、表征和研究高温超导体（如铜酸盐）的性质，采用电子双层晶体管（EDLT）技术，使用离子液体作为栅极电介质，其载流子浓度将在场效应晶体管几何形状中发生静电改变。实际上，静电掺杂将取代化学掺杂。由于载流子浓度是控制这些系统性质的控制参数，因此这种方法将有助于通过载流子浓度的连续和可逆变化来研究系统。该计划包括x射线散射和超流体密度的研究，以补充通常的电输运和磁输运测量。电子双层晶体管包含一个栅极，一个电荷可以积聚或耗尽的层，源极和漏极，以及测量纵向和横向电压的电极。离子液体是由大离子组成的熔盐，它们的库仑相互作用足够小，使它们成为室温液体。在施加栅极电压时，离子移动到要掺杂的层的表面，形成一个双电层，这样随着电荷的诱导，就像纳米级厚度的电容器一样。使用edlt形成的电荷积累层或耗尽层厚度可能只有几个单元格的量级，并且将包含高电场和电场梯度。掺杂层可以是二维超导体而不是三维超导体。因此，在相同的电荷水平上，静电掺杂不能完全等同于化学掺杂。另一方面，当电场掺杂的微观过程被很好地理解时，对铜酸盐的丰富物理特性可能会有相当大的了解。这个材料世界网络项目将采用离子液体场效应晶体管结构来静电改变载流子密度，并研究高温超导体物理性质的由此变化。通常的方法是制备具有不同化学成分的样品。这种新方法消除了这样做的需要，加快了勘探速度。离子液体在室温下是熔盐，取代了场效应晶体管结构中的栅极绝缘体。与传统绝缘体相比，它们的使用可以促进电荷转移100倍以上，因为形成了一个电子双层，这实际上是一个纳米级间隙的电容器。拟议项目的更广泛影响包括在传统的物理博士项目中培训研究生，并为明尼苏达州和其他地方的本科生提供一个有用和积极的研究经验的场所。此外，这项国际努力将允许来自美国和西班牙的人员进行强有力的互动，这将扩大全球科学界年轻科学家的经验。最后，本提案中描述的工作可能会对寻找新的超导体产生影响，这是当代凝聚态物质和材料物理学的重大挑战之一。它可以证明静电掺杂是传统化学掺杂的可行替代方案。本项目由凝聚态物理项目和材料研究部特别项目办公室支持。

TECHNICAL SUMMARY:This Materials World Network project will synthesize, characterize and study experimentally, properties of high temperature superconductors such as the cuprates, whose carrier concentrations will be electrostatic altered in field effect transistor geometries employing an electronic double layer transistor (EDLT) technique that uses ionic liquids as gate dielectrics. In effect electrostatic doping would replace chemical doping. Since carrier concentration is a control parameter that governs the properties of these systems, this approach will facilitate the investigation of systems through continuous and reversible changes of carrier concentration. The program includes studies of X-ray scattering and superfluid density to supplement the usual measurements of electrical transport and magneto-transport. Electronic double layer transistors contain a gate electrode, a layer into which charge can be accumulated or depleted, source and drain electrodes, as well as electrodes for measuring longitudinal and transverse voltages. Ionic liquids are molten salts consisting of large ions such that their Coulomb interaction is sufficiently small to make them room temperature liquids. Upon applying a gate voltage, ions move to the surface of the layer to be doped, forming an electric double layer such that with the charge induced, acts as a capacitor of nanoscale thickness. The charge accumulation or depletion layers formed using EDLTs may be the order of just a few unit cells in thickness and will contain high electric fields and electric field gradients. The doped layer may be a two-dimensional rather than a three-dimensional superconductor. It is thus not a given that electrostatic doping is completely equivalent to chemical doping to the same charge level. On the other hand, when the microscopic process of electric field doping becomes well understood, considerable insight into the rich physics of the cuprates may be gained. NON-TECHNICAL SUMMARYThis Materials World Network project will employ ionic liquid field effect transistor configurations to electrostatically alter charge carrier densities, and study the resultant changes in the physical properties of high temperature superconductors. The usual approach to this is to prepare samples with different chemical compositions. This new approach eliminates the need to do this, speeding the rate of exploration. Ionic liquids, which are molten salts at room temperature, replace the gate insulator in the field effect transistor configuration. Their use can facilitate charge transfers more than 100 times greater than achievable with conventional insulators, because of the formation of an electronic double layer, which is in effect a capacitor with a nanometer scale gap. The broader impacts of the proposed program include training of graduate students in a traditional physics Ph.D. program and providing a venue for useful and positive research experiences for undergraduates from both Minnesota and elsewhere. In addition, this international effort will allow for strong interaction of personnel from the US and Spain, which will broaden the experience of young scientists in the global scientific community. Finally, the work described in this proposal may have an impact on the search for new superconductors, which is one of the grand challenges of contemporary condensed matter and materials physics. It could demonstrate that electrostatic doping is a viable alternative to traditional chemical doping in this quest. This project is supported by the Condensed Matter Physics program and the Office of Special Programs, Division of Materials Research.