NV centers as local probes of two-dimensional materials

Abstract

Over the past decade, Nitrogen Vacancy (NV) color centers in diamond have emerged as powerful tools for quantum simulation and metrology. These atom-like defects, while confined to the diamond lattice, exhibit many properties of trapped atoms including optical transitions and high sensitivity to magnetic fields. These properties, combined with their small scale, has led to many applications for NV centers as sensors biology, chemistry, and condensed matter physics. In this thesis, we use NV centers to study a number of two dimensional systems, including Van der Waals heterostructures and the surface of the diamond itself. First, we correlate NV center measurements with various surface sensitive spectroscopy techniques to identify and mitigate deleterious sources of noise at the surface. We use this information to develop a surface treatment that extends the coherence time of shallow NV centers, which is necessary for most sensing applications. We then investigate a particular system of defects hosted at the diamond surface, the g=2 ``dark'' surface spins, and determine their properties through coherence measurements of shallow NV centers. We find that the characteristic shape of the coherence decay can itself be used as a sensor, as it encodes information about the dynamical nature of the sensing target as well as the distance between the NV center sensor and the two dimensional surface. We then turn to measuring electronic properties of 2D heterostructures composed of graphene and hexagonal boron nitride. By mapping out the spatial dependence of magnetic noise due to phonon scattering in a highly biased graphene field effect transistor, we discover a previously undescribed electron-phonon instability in graphene that is analogous to amplified spontaneous emission in a laser. Finally, we use NV centers to measure the gate dependent orbital magnetic response of a single sheet of graphene through a gate modulation lock-in technique. The ability to measure local magnetic properties of 2D materials with NV centers will likely find many uses in future experiments, as they are compatible with traditional transport techniques and provide spatially resolved information even in devices with inhomogenous properties.