Utsab Banerjee (Technical University of Munich, Germany)
LinkedIn: Utsab Banerjee, X: @UtsabBan1729, BlueSky: @utsab1729.bsky.social
Abstract: Nitrogen-vacancy (NV) centres in diamond are powerful quantum sensors capable of performing NMR spectroscopy on spin systems far beyond the reach of conventional inductive detection. Positioned a few nanometers beneath the diamond surface, these optically addressable defects sense statistical nuclear spin fluctuations from nanoscale volumes, circumventing the Boltzmann polarisation bottleneck that demands large samples and high magnetic fields. Deuterium (²H) is an ideal target: its quadrupolar Pake patterns encode molecular geometry and dynamics, with intrinsic breadths naturally matching NV-accessible spectral resolution. Resolving such lineshapes at the nanoscale has remained an outstanding challenge.
Here, we demonstrate nanoscale ²H NMR using shallow NV centre ensembles in an isotopically enriched diamond chip, at magnetic fields orders of magnitude lower than conventional spectrometers. Correlation spectroscopy protocols built on dynamical decoupling sequences yield powder-like ²H quadrupolar Pake patterns from deuterated samples on the diamond surface, directly comparable to bulk solid-state ²H NMR.
NV-NMR delivers a spin sensitivity many orders of magnitude beyond conventional inductive detection while retaining the rich spectral information of the quadrupolar interaction, fittable with standard solid-state NMR software. Variable-temperature measurements reveal distinct interfacial physics: the polymer shows suppressed dynamics consistent with an elevated local glass-transition temperature at the diamond surface, while the molecular solid undergoes a progressive lineshape collapse tracking its solid-liquid phase transition. This work establishes NV-based quadrupolar ²H NMR as a new sensing modality for probing molecular dynamics at surfaces and interfaces, with ultimate prospects for single-molecule detection.
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