Break up of heavy fermions at an antiferromagnetic instability

TL;DR

This paper investigates the electronic and magnetic phase transitions in YbRh2Si2, providing evidence for a Kondo-breakdown quantum critical point and exploring how chemical pressure affects magnetic instabilities and non-Fermi-liquid behavior.

Contribution

It offers high-resolution measurements supporting the existence of a Kondo-breakdown quantum critical point and discusses how chemical substitution influences magnetic and electronic phases.

Findings

Support for a Kondo-breakdown quantum critical point

Chemical pressure affects magnetic order stability

Moderate Ir substitution induces a non-Fermi-liquid phase

Abstract

We present results of high-resolution, low-temperature measurements of the Hall coefficient, thermopower, and specific heat on stoichiometric YbRh2Si2. They support earlier conclusions of an electronic (Kondo-breakdown) quantum critical point concurring with a field induced antiferromagnetic one. We also discuss the detachment of the two instabilities under chemical pressure. Volume compression/expansion (via substituting Rh by Co/Ir) results in a stabilization/weakening of magnetic order. Moderate Ir substitution leads to a non-Fermi-liquid phase, in which the magnetic moments are neither ordered nor screened by the Kondo effect. The so-derived zero-temperature global phase diagram promises future studies to explore the nature of the Kondo breakdown quantum critical point without any interfering magnetism.