Piezoelectric microresonators for sensitive spin detection

TL;DR

This paper explores the potential of piezoelectric microresonators at GHz frequencies for sensitive spin detection, demonstrating surface magnetic fields and discussing prospects for single-spin electrical detection at cryogenic temperatures.

Contribution

It introduces the concept of GHz surface magnetic fields in piezoelectric microresonators and demonstrates their existence through experiments with YIG spheres, proposing new avenues for spin detection.

Findings

Surface magnetic fields scale as the square of frequency.

Excess power absorption observed when YIG sphere is in the evanescent field.

Feasibility of electrical detection of single spins at cryogenic temperatures.

Abstract

Piezoelectric microresonators are indispensable in wireless communications, and underpin radio frequency filtering in mobile phones. These devices are usually analyzed in the quasi-(electro)static regime with the magnetic field effectively ignored. On the other hand, at GHz frequencies and especially in piezoelectric devices exploiting strong dimensional confinement of acoustic fields, the surface magnetic fields ($B_{1}$) can be significant. This $B_1$ field, which oscillates at GHz frequencies, but is confined to ${\mu}$m-scale wavelengths provides a natural route to efficiently interface with nanoscale spin systems. We show through scaling arguments that $B_1{\propto}f^2$ for tightly focused acoustic fields at a given operation frequency $f$. We demonstrate the existence of these surface magnetic fields in a proof-of-principle experiment by showing excess power absorption at the focus of a surface acoustic wave (SAW), when a polished Yttrium-Iron-Garnet (YIG) sphere is positioned in the evanescent field, and the magnon resonance is tuned across the SAW transmission. Finally, we outline the prospects for sensitive spin detection using small mode volume piezoelectric microresonators, including the feasibility of electrical detection of single spins at cryogenic temperatures.