1302.5908 (Yusuke Nishida)

Electron spin resonance in a dilute magnon gas as a probe of magnon
scattering resonances    [PDF]

Yusuke Nishida

We study the electron spin resonance in a dilute magnon gas that is realized in a ferromagnetic spin system at low temperature. A quantum cluster expansion is developed to show that the frequency shift of the single-magnon peak changes its sign and the linewidth reaches its maximum across a scattering resonance between magnons. Such characteristic behaviors are universal and can be used to experimentally locate the two-magnon resonance when an external parameter such as pressure is varied. Future achievement of the two-magnon resonance may have an impact comparable to the Feshbach resonance in ultracold atoms and will open up a rich variety of strongly correlated physics such as the recently proposed Efimov effect in quantum magnets. We also suggest that the emergence of an Efimov state of three magnons may be observed with the electron spin resonance through an additional peak structure in the linewidth caused by the three-magnon resonance.

View original: http://arxiv.org/abs/1302.5908