By Qnami
The team led by Prof. van der Sar fabricated a device where spin waves travel in Yttrium Iron Garnet (YIG). They placed a diamond membrane with NV centers on top to be able to image the spin waves. With this, they could observe that a stripe of molybdenum–rhenium (MoRe) modifies the wavelength of the spin waves once it turns superconducting when cooled down. This is explained by the Meissner effect, by which superconductors expel magnetic fields from their interior. To do so, they generate currents that counter-act the applied field, the so-called Meissner-currents. The stray fields generated by a spin wave thus leads to Meissner currents in the superconductor, which in turn modifies the spin-wave, forming a hybrid spin-wave-Meissner-current mode. The wavelength of this mode as a function of external parameters such as magnetic field and temperature is then imaged by the NV centers. They also reveal how deep the magnetic field penetrates the superconductor, that is an alternative method to measure the London penetration depth. The work by M. Borst and co-workers highlights that NV magnetometry will play a crucial role in proving the functionality of such future spin-wave devices. The spin-waves used in this work have wavelengths in the micrometer-range, thus it was possible to image them using widefield NV magnetometry.
