Propagating spin-wave spectroscopy in nanometer-thick YIG films at millikelvin temperatures

TL;DR

This study demonstrates the successful propagation of spin waves in 100 nm thick YIG films at millikelvin temperatures, paving the way for integrated magnonic quantum technologies.

Contribution

We demonstrate spin-wave propagation in ultra-thin YIG films at millikelvin temperatures using nanoantennas, with results aligning with theoretical predictions, enabling quantum magnonic applications.

Findings

Spin-wave transmission over 10 μm distance at 45 mK.

Agreement of measured group velocity and magnetisation with theory.

Substrate effects are negligible below 75 mT magnetic field.

Abstract

Performing propagating spin-wave spectroscopy of thin films at millikelvin temperatures is the next step towards the realisation of large-scale integrated magnonic circuits for quantum applications. Here we demonstrate spin-wave propagation in a $100\,\mathrm{nm}$-thick yttrium-iron-garnet film at the temperatures down to $45 \,\mathrm{mK}$, using stripline nanoantennas deposited on YIG surface for the electrical excitation and detection. The clear transmission characteristics over the distance of $10\,\mu \mathrm{m}$ are measured and the subtracted spin-wave group velocity and the YIG saturation magnetisation agree well with the theoretical values. We show that the gadolinium-gallium-garnet substrate influences the spin-wave propagation characteristics only for the applied magnetic fields beyond $75\,\mathrm{mT}$, originating from a GGG magnetisation up to $47 \,\mathrm{kA/m}$ at $45 \,\mathrm{mK}$. Our results show that the developed fabrication and measurement methodologies enable the realisation of integrated magnonic quantum nanotechnologies at millikelvin temperatures.