A micro-coil diamond anvil cell platform for NMR/NQR measurement

Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) at multi-GPa pressures are typically constrained by tiny sample volumes and limited RF sensitivity. We present a simple, reproducible micro-coil diamond-anvil-cell (DAC) platform that enables quantitative NMR/NQR on real materials to up to 10 GPa, where a lab-made solenoidal micro-coil is seated in the apertured gasket to maximize filling factor while reducing contributions from magnetic backgrounds. As a proof of principle, the ⁶³Cu NQR of Cu₂O was measured, showing excellent agreement with the pressure estimated from ruby fluorescence and good pressure uniformity to ~7 GPa. We also apply this platform to SrRh₂P₂, a clean 122-type benchmark for tracking how pressure-induced interlayer P-P bonding drives the un-collapsed tetragonal to collapsed-tetragonal transition and reconstructs the low-energy electronic states. Above ~5 GPa, the ³¹P Knight shift exhibits a discontinuous drop, consistent with a sudden reduction of N(E_F) and of the uniform (q = 0) spin susceptibility due to enhanced interlayer bonding; correspondingly, 1/T₁T is clearly enhanced, while 1/T₂ remains nearly constant on approach to the transition ~5 GPa. These NMR findings are in excellent agreement with our high pressure single-crystal XRD and electrical transport data. Overall, this platform bridges the gap between relatively straightforward piston-cylinder NMR/NQR experiments (< 2.5 GPa) and complex high-pressure probes, is readily applicable to a broad class of quantum materials with suitable NMR/NQR isotopes and is extendable to higher pressures via planar coils and optimized gasket geometries.