# Fermi surface enlargement on the Kondo lattice

## TL;DR

This paper introduces a new formalism for the Kondo lattice model using non-canonical degrees of freedom based on su(2|2) algebra, providing a novel perspective on heavy fermion formation and explaining experimental observations.

## Contribution

The authors develop a non-canonical formalism using su(2|2) algebra to analyze the Kondo lattice, offering a new approach beyond slave-particle methods.

## Key findings

- Enlargement of the Fermi surface in the Kondo lattice.
- Violation of the Luttinger sum rule in this formalism.
- Interpretation of photoemission experiments on Ce-115 systems.

## Abstract

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 new formalism, based instead on non-canonical degrees of freedom. We demonstrate that the graded Lie algebra su(2|2) provides a powerful means of organizing correlations on the Kondo lattice through a splitting of the electronic degree of freedom, in a manner which entwines the conduction electrons with the local moment spins. This offers a novel perspective on heavy fermion formation. Unlike slave-particle methods, non-canonical 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.