Probing quasi two-dimensional materials using Nuclear Magnetic Resonance*

Our ability to design and produce a variety of thin films and two-dimensional materials has greatly evolved during the last two decades. This technical breakthrough allows for the study of physical properties that do not transpose to bulk materials. The fragility and complexity of such materials require technological improvements to characterize samples without causing damage to them. Nuclear Magnetic Resonance (NMR) is a well-known technique used to probe local magnetism in a great variety of materials and requires no direct contact to the studied samples. However, conventionally, this technique requires a large number of spins (10^20) in order to be efficient, which can be partially solved by decreasing the temperature and increasing the applied magnetic field. This limits the accessibility of the phase diagram and the study of magnetic phase transitions of materials. Here, we demonstrate that planar superconducting NbN resonators in proximity to the surface of a thin sample can be used has an alternative to standard coils for NMR measurements. These devices allow for improved sensitivity NMR measurements of thin films at low temperatures and pave the way towards probing atomically thin samples. This technique is also easily implemented within a conventional solid-state NMR set-up.