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Nanoscale magnetometry with a single spin in diamond at cryogenic temperatures

Thiel, Lucas. Nanoscale magnetometry with a single spin in diamond at cryogenic temperatures. 2019, Doctoral Thesis, University of Basel, Faculty of Science.

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Official URL: http://edoc.unibas.ch/diss/DissB_13235

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Abstract

Individual electronic spins can yield close-to-ideal magnetometers to investigate magnetic phenomena on the nanoscale. Spins offer sensitivity to magnetic fields by virtue of the Zeeman effect and can be localized to atomic length scales, which enables nanoscale resolution in imaging. The electronic spin of the Nitrogen-Vacancy (NV) center in diamond has been identified as a particularly fruitful system to implement these concepts, as its additional ability of optical spin initialization and readout renders the NV center a non-invasive and quantitative magnetometer with single-spin sensitivity and nanoscale spatial resolution. Nitrogen-Vacancy based magnetometry has been widely exploited exclusively under ambient conditions. Advancing the frontiers of nanoscience at low temperature, however, hinges on the availability of novel sensors for nanoscale imaging such as the Nitrogen-Vacancy center.
To fill this gap, in this thesis we developed and employed an NV-based scanning magnetometer at cryogenic temperatures. We present the implementation of an atomic force microscope, which is functionalized with a single NV center, situated in a liquid helium bath cryostat, and interfaced with a confocal microscope for optical initialization and readout of the NV's electronic spin. We demonstrate DC magnetic field sensitivities better than uT/sqrt(Hz) and an unprecedented spatial resolution of 30 nm. Moreover, we introduce powerful post-processing techniques and employ them on the recorded quantitative magnetic stray field maps. This allows for the retrieval of important material parameters by recovering the underlying planar current distribution or spin texture.
To demonstrate the performance of our cryogenic magnetometer, we focused on nanoscale studies of magnetic phenomena in superconductors. We were able to image stray fields of individual vortices with highest spatial resolution and perform nanoscale studies of the Meissner effect in superconductor nanostructures. Both of these measurements enabled the unambiguous determination of the London penetration depth, allowed for the inspection of nanoscale defects inhibiting superconductivity and for benchmarking competing, microscopic models for supercurrent flow.
In a second experiment, the application of the cryogenic scanning setup to recently discovered two-dimensional magnets in van der Waals heterostructures led to one of the key results of this thesis. We quantitatively determined the magnetization of a monolayer CrI3 and demonstrated that the magnetic coupling between individual layers in a multi-layer stack CrI3 is intimately connected to the material structure, and that structural modifications can induce a relaxation to the magnetic ground state, which has not been observed so far in this material.
Our results therefore illustrate the power of NV magnetometry in exploring local magnetic properties of electronic systems with high resolution, and the great potential for future nanoscale explorations of a large range of complex, condensed matter systems at cryogenic temperatures.
Advisors:Maletinsky, Patrick and Jacques, Vincent
Faculties and Departments:05 Faculty of Science > Departement Physik > Physik > Georg H. Endress-Stiftungsprofessur für Experimentalphysik (Maletinsky)
UniBasel Contributors:Thiel, Lucas
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:13235
Thesis status:Complete
Bibsysno:Link to catalogue
Number of Pages:1 Online-Ressource (m, 112, XXIV Seiten)
Language:English
Identification Number:
Last Modified:19 Aug 2019 13:06
Deposited On:19 Aug 2019 13:05

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