High-pressure charge distribution in YBa2Cu3O6+y by NMR

我们建议定量地确定外加压力如何改变铜酸盐高温超导体YBa2Cu3O6+y中CuO2平面内的局域电荷分布。压力，无论是化学诱导的还是外加的，在铜酸盐物理中都具有非常重要的作用，因为它不仅导致这些材料的超导临界温度(T_C)最高，甚至导致了新材料的发现。然而，目前还不清楚压力如何影响铜酸盐性质的变化。核磁共振在铜酸盐研究中是一个非常强大的探针，但它在必要的高压下的使用直到最近才开始出现。在2011年的第一次实验中，我们用YBa2Cu4O8的17O核磁共振显示了新的能力，在大约7 GPa时，我们观察到伪隙特征的消失。与此同时，我们已经成为高压核磁共振领域的世界领先企业，开发了自己的高压核磁共振池，并展示了它们在单晶材料中的应用。此外，在2014年，我们表明，在铜和O的核磁共振四极分裂提供了所有铜酸盐中CuO2平面上的局部电荷的定量测量，并且这种分布设定了最大可达到的T_c。这将电荷分布与超流密度联系在一起，这是一个材料化学参数，超流密度是在超导体样品中在非常低的温度下测量的属性，再现了上村著名的关系。因此，我们现在能够找出在压力显著改变T_c的情况下，电荷的变化及其在铜酸盐中的分布。通过拟议的研究，将揭示是否确实是掺杂的变化或铜和氧之间的平面内电荷重新分配，或者被认为与超导竞争的电荷顺序的抑制导致了T_c的变化。这些结果不仅将阐明压力在铜酸盐物理中的作用，而且还有助于理解是什么设定了最大的T_c。此外，我们将能够定量地研究这些材料中可能形成的静态电荷密度波，以及它们对外部压力的响应。

We propose to quantitatively determine how the application of external pressure changes the local charge distribution in the CuO2 plane in the cuprate high-temperature superconductor YBa2Cu3O6+y. Pressure, chemically induced as well as externally applied, has a very prominent role in cuprate physics, since it not only induces the highest critical temperatures of superconductivity (Tc) in these materials, but even led to the discovery of new materials. However, it is not clear how pressure affects the changes in the properties of the cuprates. NMR is a very powerful probe in cuprate research, but its use with the necessary high pressures became available only very recently. In a first experiment in 2011, we showed the new capability with 17O NMR of YBa2Cu4O8 where we observed the vanishing of the pseudo gap features at about 7 GPa. Meanwhile, we have become world-leading in high-pressure NMR, having developed our own high-pressure NMR cells and also demonstrated their use with single crystal materials. Moreover, in 2014 we showed that the NMR quadrupole splittings at Cu and O provide a quantitative measure of local charges in the CuO2 plane in all cuprates, and that this distribution sets the maximum achievable Tc. This relates the charge distribution, which is a material chemistry parameter, to the superfluid density, a property measured at very low temperatures in superconducting samples, reproducing Uemura's famous relation. Consequently, we are now in a position to find out what happens to the charge and its distribution in the cuprates at pressures that change Tc significantly. With the proposed research it will be revealed whether indeed a change in doping or an intraplanar charge redistribution between Cu and O, or suppression of charge order that is believed to compete with superconductivity is responsible for the change in Tc. The results will not only clarify the role of pressure in cuprate physics, but also help in understanding what sets the maximum Tc. Furthermore, we will be able to quantitatively investigate a possible formation of static charge density waves in these materials, and their response to external pressure.