High-pressure charge distribution in YBa2Cu3O6+y by NMR

我们建议定量地确定如何应用外部压力的变化的局部电荷分布在氧化铜平面中的铜酸盐高温超导体YBa_2Cu_3O_6 +y。压力，化学诱导以及外部施加，在铜氧化物物理学中具有非常突出的作用，因为它不仅在这些材料中诱导超导性的最高临界温度（Tc），而且甚至导致新材料的发现。然而，目前尚不清楚压力如何影响铜酸盐性质的变化。核磁共振是一个非常强大的探针在铜酸盐的研究，但它的使用与必要的高压成为最近才可用。在2011年的第一个实验中，我们用YBa2Cu4O8的17O NMR展示了新的能力，我们观察到赝能隙特征在大约7 GPa时消失。与此同时，我们已经成为世界领先的高压NMR，开发了我们自己的高压NMR单元，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Cu和O的NMR四极分裂提供了在所有铜酸盐的CuO 2平面中的局部电荷的定量测量，并且这种分布设定了最大可实现的Tc。这将电荷分布（材料化学参数）与超流密度（超导样品在极低温度下测量的特性）联系起来，再现了Uemura的著名关系。因此，我们现在能够找出在显著改变Tc的压力下铜酸盐中电荷及其分布发生了什么。随着拟议的研究，它将揭示是否确实是掺杂或铜和O之间的平面内电荷重新分配的变化，或被认为是与超导性竞争的电荷顺序的抑制是负责Tc的变化。结果不仅将澄清压力在铜酸盐物理中的作用，而且有助于理解是什么设定了最大Tc。此外，我们将能够定量研究这些材料中静电荷密度波的可能形成，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.