Fermi surface enlargement on the Kondo lattice

The Kondo lattice model is a paradigmatic model for the description of local moment systems, a class of materials exhibiting a range of strongly correlated phenomena including heavy fermion formation, magnetism, quantum criticality, and unconventional superconductivity. Conventional theoretical approaches invoke fractionalization of the local moment spin through large-N and slave particle methods. In this work we develop a formalism based on noncanonical degrees of freedom, building upon a recently developed approach for strongly correlated electrons [E. Quinn, Phys. Rev. B 97, 115134 (2018)10.1103/PhysRevB.97.115134]. Specifically, we demonstrate that higher dimensional representations of su(2|2) correspond to a splitting of the electronic degree of freedom on the Kondo lattice, in a manner which entwines the conduction electrons with the local moment spins. This provides a powerful means of organizing correlations, and offers a perspective on heavy fermion formation. Unlike slave-particle methods, noncanonical degrees of freedom generically allow for a violation of the Luttinger sum rule, and we interpret recent angle resolved photoemission experiments on Ce-115 systems in view of this.