Spontaneous interlayer coherence in bilayer Kondo systems

TL;DR

This paper explores the phase diagram of bilayer Kondo systems, revealing a spontaneous interlayer coherence phase that breaks symmetry and mediates a transition between two distinct Fermi liquid states.

Contribution

It introduces the concept of a spontaneous interlayer phase coherence in bilayer Kondo systems and analyzes its role in quantum phase transitions.

Findings

Identification of a spontaneous interlayer coherence phase

Existence of a finite-temperature Kosterlitz-Thouless transition

Phase diagram illustrating transitions between Fermi liquid states

Abstract

Bilayer Kondo systems present interesting models to illustrate the competition between the Kondo effect and intermoment exchange. Such bilayers can exhibit two sharply distinct Fermi liquid phases which are distinguished by whether or not the local moments participate in the Fermi sea. We study these phases and the evolution from one to the other upon changing Kondo coupling. We argue that an ordered state with spontaneous interlayer phase coherence generically intervenes between the two Fermi liquids. Such a condensate phase breaks a U(1) symmetry and is bounded by a finite-temperature Kosterlitz-Thouless transition. Based on general arguments and mean-field calculations we investigate the phase diagram and associated quantum phase transitions.