All-Optical dc Nanotesla Magnetometry Using Silicon Vacancy Fine Structure in Isotopically Purified Silicon Carbide

Abstract

We uncover the fine structure of a silicon vacancy in isotopically purified silicon carbide (4H-SiC28 ) and reveal not yet considered terms in the spin Hamiltonian, originated from the trigonal pyramidal symmetry of this spin-3/2 color center. These terms give rise to additional spin transitions, which would be otherwise forbidden, and lead to a level anticrossing in an external magnetic field. We observe a sharp variation of the photoluminescence intensity in the vicinity of this level anticrossing, which can be used for a purely all-optical sensing of the magnetic field. We achieve dc magnetic field sensitivity better than 100nT/Hz within a volume of 3×10−7mm3 at room temperature and demonstrate that this contactless method is robust at high temperatures up to at least 500 K. As our approach does not require application of radio-frequency fields, it is scalable to much larger volumes. For an optimized light-trapping waveguide of 3mm3 , the projection noise limit is below 100fT/Hz .

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Plain Language Summary

Precise measurements of magnetic fields are required in many applications from space science to medicine and nanotechnology. One of the standard approaches to realize highly sensitive chip-scale magnetometry is based on the optically detected magnetic resonance of color centers in solids. In this technique, intense radio-frequency pulses are applied to manipulate spin states subject to the external magnetic field, which are then read out optically. Here, we demonstrate an alternative method for magnetic-field sensing that does not require radio-frequency fields. This method is based on sharp variations in the photoluminescence intensity with magnetic field, associated with atom-size defects in silicon carbide. Using this straightforward approach, we achieve 100-nT dc magnetic-field resolution within a 1000μm3 detection volume for an integration time of 1 s.

The pronounced variations in the photoluminescence intensity that we observe are caused by level anticrossings and are related to additional terms in the spin Hamiltonian associated with the trigonal pyramidal symmetry of the silicon vacancy defects in silicon carbide. These terms have not been considered thus far, and they also explain the puzzling observation of the spin transitions with the change of the spin projection quantum number equal to ±2 (i.e., the transitions that are typically forbidden). We show that since these effects are a basic property of any spin-3/2 system possessing low symmetry, our approach can be applied to many other similar defect centers in wide-band-gap materials as well as to quantum dots. The demonstrated method is robust up to at least 500 K, which suggests that it is a simple, contactless method to monitor weak magnetic fields over a broad temperature range, particularly when radio-frequency fields cannot or should not be applied. For an optimized light-trapping waveguide of 1mm3 , we expect that magnetic fields in the subpicotesla range can be detected within 1 s.

We anticipate that our findings will pave the way for experimental applications in detecting magnetic fields in biomedicine and geophysics.