Electrical detectability of magnon-mediated spin current shot noise

Abstract

A magnonic spin current crossing a ferromagnet-metal interface is accompanied by spin current shot noise arising from the discrete quanta of spin carried by magnons. In thin films, e.g., the spin of so-called squeezed magnons have been shown to deviate from the common value $\hslash$, with corresponding changes in the spin noise. In experiments, spin currents are typically converted to charge currents via the inverse spin Hall effect. We here analyze the magnitude of the spin current shot noise in the charge channel for a typical electrically detected spin pumping experiment, and find that the voltage noise originating from the spin current shot noise is much smaller than the inevitable Johnson-Nyquist noise. Furthermore, we find that due to the local nature of the spin-charge conversion, the ratio of spin current shot noise and Johnson-Nyquist noise cannot be systematically enhanced by tuning the sample geometry, in contrast to the linear increase in dc spin pumping voltage with sample length. Instead, the ratio depends sensitively on material-specific transport properties. Our analysis thus provides guidance for the experimental detection of squeezed magnons through spin pumping shot noise.

Revised manuscript title, added paragraph of interpretation of the shot noise enhancement with temperature, added brief discussion of the low temperature limit, references added

References in corpus (7)

• Theory of spin Hall magnetoresistance
• Temperature dependence of spin diffusion length and spin Hall angle in Au and Pt
• Planck Spectroscopy and the Quantum Noise of Microwave Beam Splitters
• Magnon-squeezing as a niche of quantum magnonics
• Spin current noise of the spin Seebeck effect and spin pumping
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• Spin Hall noise

Cited by in corpus (1)

• Magnonic spin current shot noise in an itinerant Fermi gas