Superconductor-Insulator Transitions

摘要：本研究支持了元素和化合物超薄膜超导体-绝缘体跃迁的实验研究。了解它们的性质很重要，部分原因是它们在高温超导中的作用。它们是当代凝聚态物理的一个重要范例的最简单的例子，连续量子相变，与热转变相反，发生在零温度下，但在非零温度下具有可测量的特征，用于表征它们。在超导体-绝缘体跃迁的情况下，基态随系统外部参数的变化而变化，如平行或垂直的磁场、无序或载流子密度。在其他表现出量子相变的系统中，有吸附在随机衬底上的4He、二维电子气体、许多复杂的强相关电子材料和冷原子的构型，它们可以有效地用于模拟许多凝聚态现象。超导体-绝缘体转变的研究需要先进的实验科学工具，如薄膜生长、纳米制造和超低温测量技术。该项目支持博士和本科生的培养，为科学事业做好准备。PI的主要外展活动是教授新生研讨会。技术摘要：该研究旨在确定涉及不同材料和调谐参数的各种超导体-绝缘体转变的相关机制。它涉及四个不同的调查。第一项研究是尝试观察无序薄膜中的超导体-绝缘体跃迁是否可以通过可调谐的近似二维电子气体提供的耗散来系统地调谐。第二项研究是使用交流技术测量超电子密度薄膜的电荷密度依赖性，在一个载流子浓度范围内，富氧化合物La2CuO4+x （LCO）薄膜使用离子液体进行静电掺杂。第三个研究方向是测量淬火金属薄膜超导体-绝缘体过渡附近的非平衡电流噪声谱密度，第四个研究方向是研究垂直场调谐的淬火金属薄膜超导体-绝缘体过渡，目的是确定量子临界点处的极限电阻是否为对的量子电阻。以及这些材料中是否存在霍尔绝缘体，就像氧化铟等化合物中明显存在的那样。

Non-Technical Abstract:This research supports the experimental investigation of superconductor-insulator transitions of ultrathin films of elements and compounds. Understanding their nature is important, in part because of their role in high temperature superconductivity. They are the simplest examples of an important paradigm of contemporary condensed matter physics, continuous quantum phase transitions, which in contrast with thermal transitions, occur at zero temperature, but have measurable signatures at nonzero temperatures, which are used to characterize them. In the case of the superconductor-insulator transition, the ground state is changed in response to the variation of an external parameter of the system, such as parallel or perpendicular magnetic field, disorder, or carrier density. Among other systems exhibiting quantum phase transitions are 4He adsorbed on random substrates, two-dimensional electron gases, numerous complex strongly correlated electron materials, and configurations of cold atoms, which can be effectively used to model many condensed matter phenomena. The study of superconductor-insulator transitions requires advanced tools of experimental science such as film growth, nanofabrication and ultra-low temperature measurement techniques. This project supports the training of both Ph.D. and undergraduate students that is excellent preparation for a scientific career. The primary outreach activity of the PI is the teaching of freshman seminars.Technical Abstract:The research is directed at identifying the mechanisms associated with a variety of superconductor-insulator transitions involving different materials and tuning parameters. It involves four distinct investigations. The first investigation is an attempt to see whether a superconductor-insulator transition in a disordered thin film can be systematically tuned by dissipation provided by a tunable, proximate two-dimensional electron gas. The second investigation is the measurement of the charge-density dependence of films of the super-electron density using an AC technique, over a range of carrier concentrations of films of the oxygen-enriched compound, La2CuO4+x (LCO) which are electrostatically doped using ionic liquids. The third thrust is the measurement of the out-of-equilibrium, current noise spectral density near the superconductor-insulator transition of quench-deposited metal films, and the fourth direction of research is the study of the perpendicular-field tuned superconductor-insulator transition of quench-deposited metal films with the goal of determining whether the limiting resistance at the quantum critical point is the quantum resistance for pairs, and whether there is a Hall insulator in these materials, as is apparently present in the case of compounds such as indium oxide.