Spatiotemporal buildup of the Kondo screening cloud

Abstract

We investigate how the Kondo screening cloud builds up as a function of space and time. Starting from an impurity spin decoupled from the conduction band, the Kondo coupling is switched on at time $t=0$. We work at the Toulouse point where one can obtain exact analytical results for the ensuing spin dynamics at both zero and nonzero temperature $T$. For $t>0$ the Kondo screening cloud starts building up in the wake of the impurity spin being transported to infinity. In this buildup process the impurity spin--conduction band spin susceptibility shows a sharp light cone due to causality, while the corresponding correlation function has a tail outside the light cone. At $T=0$ this tail has a power-law decay as a function of distance from the impurity, which we interpret as due to initial entanglement in the Fermi sea.