Universal Spin Screening Clouds in Local Moment Phases

TL;DR

This paper reveals the universal properties of local moment spin clouds in phases where impurity spins are unscreened, showing their algebraic or exponential decay depending on the conduction electrons' density of states, supported by theory and numerics.

Contribution

It introduces the concept of a universal LM cloud with a characteristic length scale, extending understanding of impurity spin behavior in various electronic environments.

Findings

LM clouds form in local moment phases with distinct decay behaviors

Existence of a universal LM cloud length scale

Supported by analytic and numerical evidence

Abstract

When a local impurity spin interacts with conduction electrons whose density of states (DOS) has a (pseudo)gap or diverges at the Fermi energy, a local moment (LM) phase can be favored over a Kondo phase. Theoretically studying quantum entanglement between the impurity and conduction electrons, we demonstrate that conduction electrons form an ''LM spin cloud'' in general LM phases, which corresponds to, but has fundamental difference from, the Kondo cloud screening the impurity spin in the Kondo phase. The LM cloud algebraically decays over the distance from the impurity when the DOS has a pseudogap or divergence, and exponentially when it has a hard gap. We find an ''LM cloud length'', a single length scale characterizing a universal form of the LM cloud. The findings are supported by both of analytic theories and numerical computations.