EAGER: Exploring the Role of Copper Sulfides in Room Temperature Superconductors

非技术概述材料使技术进步成为可能。例如，笔记本电脑和智能手机内部的电池材料通过对这些电子设备进行充电和充电来实现它们的便携性。风车中的磁性材料使它们能够利用风力发电，为家庭和企业提供电力。长期以来，研究材料的科学家一直梦想着发现一种可以同时实现多种技术的技术。这样一种神奇的物质存在于超导体中。它将使能源、人类健康和计算技术的应用成为可能。在上个世纪，已经发现了许多这样的超导体，但它们都有一个重大挫折。这些材料只有在极低的温度下才能成为超导体。这些温度甚至低于地球上有记录以来的最低温度。此外，少数在室温附近超导的材料需要的压力只在行星中心附近才能找到。因此，科学家们长期寻求的目标是找到一种在常温和地球表面压力下有效超导体的材料。这一热切的奖项得到了美国国家科学基金会材料研究部固态和材料化学计划的支持，将研究由铜和硫组成的副产品在2023年成为这样一种奇迹材料的样本中所起的作用。这项工作包括仔细准备由铜和硫组成的样品，并在最严格的条件下对它们进行测试，以发现世界上第一个潜在的室温超导体。这一奖项由美国国家科学基金会材料研究部的固态和材料化学计划支持，将探索硫化铜在2023年报道的名为LK-99的潜在室温超导体中所起的作用。马里兰大学的研究小组进行了固态化学研究，以分离出LK-99中所含的硫化铜少数相。然而，与LK-99手稿不同的是，这里的工作假设是，这种少数相Cu2-Xs更有可能是超导体，而不是主要相氧化磷灰石，这是一种已知的宽带隙绝缘体。这一假说的形成是因为Cu2S表现出有趣的高温物理，包括上离子相变、晶体相变和绝缘体到金属的相变。后者是由铜位空位引起的空穴掺杂驱动的电子态，即Cu2-xs中的x。由于这些转变也发生在380K附近，它们解释了为什么LK-99中报道的室温超导电性应该归因于Cu2-Xs。这里的方法是通过形成Cu2-xMxS相来给这一相充电，其中M是一种与铜+价态不同的金属。这一策略类似于抑制铜酸盐和铁基超导体中的相变，即电子或空穴掺杂抑制反铁磁相变，并且在相图上出现超导区域。在Cu2S的情况下，相关的驱动力不是像在铜酸盐和铁化合物中那样的磁性，而是耦合到电子结构的离子作用力，可以驱动这种非传统的行为。这笔急切的赠款调查了不同形式的Cu2-x和Cu2-xMxS的纯样品，以了解它们的晶体、热和电子输运以及磁性如何随着x的变化而变化。研究活动使用多晶和单晶样品来确定这个阶段是否确实是理解LK-99中报告的室温迈斯纳效应的关键。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical SummaryMaterials make technological progress possible. For example, the battery materials inside laptops and smartphones enable the portability of these electronic devices by charging and recharging them. The magnetic materials in windmills allow them to harness the wind to generate the electricity that powers homes and businesses. It has long been a dream of scientists who study materials to discover one that would enable many technologies at once. Such a miracle material exists in the superconductor. It would enable applications in energy, human health, and computing technologies. In the last century, many such superconductors have been found, but they all have one major setback. These materials become superconductors only at extremely low temperatures. These temperatures are even lower than the coldest recorded temperature on Earth. Furthermore, the handful of materials that are superconducting near room temperature require pressures found only near the center of the planet. Therefore, the long-sought goal of scientists has been to find a material that is an effective superconductor near room temperature and at pressures on the surface of the Earth. This EAGER award, supported by the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, will examine the role the byproducts consisting of copper and sulfur play in a sample reported to be such a miracle material in 2023. This endeavor includes the careful preparation of samples consisting of copper and sulfur and testing them under the most rigorous conditions to uncover the world’s first potential room-temperature superconductor. Technical SummaryThis EAGER award, supported by the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, will explore the role that copper sulfides plays in the potential room-temperature superconductor called LK-99 reported in 2023. The research team at the University of Maryland carries out solid state chemistry studies to isolate the copper sulfide minority phase contained in LK-99. Unlike in the LK-99 manuscripts, however, the working hypothesis here is that it is more likely that this minority phase, Cu2-xS, is the superconductor and not the majority phase, lead oxyapatite, which is a known wide-band gap insulator. This hypothesis was formed since Cu2S displays interesting high-temperature physics including a superionic phase transition, a crystallographic phase transition, and an insulator-to-metal transition. The latter is an electronic one driven by the hole-doping brought on by copper site vacancies, which is the x in Cu2-xS. Since these transitions also occur near 380 K, they would explain why the room-temperature superconductivity reported in LK-99 should be attributed to Cu2-xS. The approach here is to charge dope this phase by forming Cu2-xMxS phases where M is a metal with a different valence state from Cu+. This strategy is similar to suppressing phase transitions in the cuprates and iron-based superconductors, whereby electron or hole doping suppresses an antiferromagnetic phase transition, and a superconducting regime appears on the phase diagram. In the case of Cu2S, the relevant driver is not magnetism as in the cuprates and iron pnictides, but rather ionic forces coupled to the electronic structure that could drive the unconventional behavior. This EAGER grant surveys phase pure samples of different forms of Cu2-xS and Cu2-xMxS to understand how their crystallographic, heat and electronic transport, and magnetic properties change as a function of x. The research activities use both polycrystalline and single crystal samples to establish whether this phase is indeed the key to understanding the room-temperature Meissner effect reported in LK-99.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.