Nanosensor for weak magnetic fields based on a Kramers-degenerate spin system $^{14}$NV–$^{13}$C

A nanosensor for weak magnetic fields based on an individual $^{14}$NV–$^{13}$C complex in diamond has been implemented, where the $^{13}$C carbon atom is located in the third coordination shell of the $^{14}$NV center. Using this sensor, the background magnetic field in the laboratory was measured: the projection onto the quantization axis of the complex $B_z$ was approximately 40 $\mu$T, which is close to the Earth's magnetic field strength. Comparative modeling of the optically detected magnetic resonance (ODMR) spectra of the $^{14}$NV and $^{14}$NV–$^{13}$C systems under various magnetic and electric fields was performed using their respective spin Hamiltonians. It was shown that employing the $^{14}$NV–$^{13}$C complex mitigates the influence of internal crystal fields on the nanomagnetometer.