Anomalous tunneling transport of spin and heat by magnonic criticality*

We present thermomagnetic transport in an ultracold atomic system with two ferromagnets linked via a magnetic quantum point contact [1]. Using the nonequilibrium field theory in the Schwinger-Keldysh formalism, we show a divergence in spin conductance and a slowing down of spin relaxation that manifest in the weak effective-Zeeman-field limit. These anomalous spin dynamics result from the magnonic critical point at which magnons become gapless due to spontaneous magnetization. Our findings unveil untapped dynamics in ultracold atomic systems, opening new avenues in thermomagnetism.