NSF Award
2403985
Non-technical Summary<br/><br/>Materials 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. <br/><br/>Technical Summary<br/><br/>This 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.<br/><br/>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.
