Impossibility of the Efimov effect for p-wave interactions

Whether the Efimov effect is possible, in principle, for p-wave or higher partial-wave interactions is a fundamental question. Recently, there has been a claim that three nonrelativistic particles with resonant p-wave interactions exhibit the Efimov effect. We point out that the assumed p-wave scattering amplitude inevitably causes a negative probability. This indicates that the Efimov states found there cannot be realized in physical situations. We also restate our previous argument that the Efimov effect, defined as an infinite tower of universal bound states characterized by discrete scale invariance, is impossible for p-wave or higher partial-wave interactions.Comment: 3 pages, no figure; published versio

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

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 how the emergence of an Efimov state of three magnons and its binding energy may be observed with the electron spin resonance.Comment: 7 pages; published versio

Transport measurement of the orbital Kondo effect with ultracold atoms

The Kondo effect in condensed-matter systems manifests itself most sharply in their transport measurements. Here we propose an analogous transport signature of the orbital Kondo effect realized with ultracold atoms. Our system consists of imbalanced Fermi seas of two components of fermions and an impurity atom of different species which is confined by an isotropic potential. We first apply a \pi/2 pulse to transform two components of fermions into two superposition states. Their interactions with the impurity atom then cause a "transport" of fermions from majority to minority superposition states, whose numbers can be measured after applying another 3\pi/2 pulse. In particular, when the interaction of one component of fermions with the impurity atom is tuned close to a confinement-induced p-wave or higher partial-wave resonance, the resulting conductance is shown to exhibit the Kondo signature, i.e., universal logarithmic growth by lowering the temperature. The proposed transport measurement will thus provide a clear evidence of the orbital Kondo effect accessible in ultracold atom experiments and pave the way for developing new insights into Kondo physics.Comment: 7 pages; published versio