Figure 2.

Local diamagnetism in La₂PrNi₂O₇ at 20 GPa. (a) Fluorescence image of sample A (La₂PrNi₂O₇ in silicon oil). The edge of the sample is outlined with a gray dashed line. The unit of the fluorescence intensity is kilo counts per second (kcps). (b, c) Typical ODMR spectra of the NV centers (b) and magnetic field mapping (c) under an external magnetic field of H_Z ∼ 120 G after ZFC of the sample to 7 K. Three points (A0, A1, A2) are selected based on their position with respect to the La₂PrNi₂O₇ sample. Point A1 is directly on the sample, A2 is at the edge of the sample and A0 is far away from the sample (serves as a reference point). The blue area in (c) shows the local diamagnetism (these points have smaller ODMR splitting than that of the reference point). (d) Local magnetic field at the NV positions as a function of the applied external magnetic field (after ZFC). For the NV centers at point A1, their local magnetic field is about 5% smaller than the applied external magnetic field. In sharp contrast, the NV centers at point A2 feel an enhanced local magnetic field. (e) Measurement protocol of ZFC-FW and FC. (f) ODMR splitting of three selected points under 120 G ZFC-FW and FC measurements. The combination of the ZFC-FW and FC curves provide clear evidence of the Meissner effect.