Fractionalization and Fermi surface volume in heavy fermion compounds: the case of YbRh$_2$ Si$_2$

TL;DR

This paper develops an effective theory for heavy fermion compounds near an antiferromagnetic transition, introducing fractionalization of heavy electrons and a new fermionic excitation to explain Fermi surface volume changes.

Contribution

It proposes a novel fractionalization scenario involving a spinless fermionic field to describe Fermi surface evolution in heavy fermion systems.

Findings

Reproduces experimental low-temperature exponents for YbRh₂(Si₁₋ₓGeₓ)₂

Provides a scenario for Fermi surface volume change across the phase diagram

Introduces a new fermionic excitation in the effective theory

Abstract

We establish an effective theory for heavy fermion compounds close to a zero temperature Anti-Ferromagnetic (AF) transition. Coming from the heavy Fermi liquid phase across to the AF phase, the heavy electron fractionalizes into a light electron, a bosonic spinon and a {\it new} excitation: a spinless fermionic field. Assuming this field acquires dynamics and dispersion when one integrates out the high energy degrees of freedom, we give a scenario for the volume of its Fermi surface through the phase diagram. We apply our theory to the special case of YbRh$_2$(Si$_{1-x}$ Ge$_x$)$_2$ where we recover, within experimental resolution, several low temperature exponents for transport and thermodynamics.