Evidence for the existence of Kondo coupled resonant modes in heavy fermions

TL;DR

This paper reports the discovery of a novel ESR signal in the heavy fermion superconductor beta-YbAlB4, revealing Kondo coupled resonant modes that exhibit dual conduction electron and local moment characteristics, shedding light on 4f-electron behavior at quantum criticality.

Contribution

It provides the first evidence of Kondo coupled resonant modes in heavy fermions, demonstrating dual ESR behavior linked to Kondo quasiparticles and quantum criticality.

Findings

Observation of ESR in beta-YbAlB4 showing dual behavior

Identification of Kondo coupled resonant modes (KCRM)

Implication of 4f-electron nature at quantum critical point

Abstract

Electron Spin Resonance (ESR) can microscopically probe both conduction electrons (ce) and local moment (LM) spin systems in different materials. A ce spin resonance (CESR) is observed in metallic systems based on light elements or with enhanced Pauli susceptibility. LM ESR is frequently seen in compounds with paramagnetic ions and localized d or f electrons. Here we report a remarkable and unprecedented ESR signal in the heavy fermion (HF) superconductor beta-YbAlB4[1] which behaves as a CESR at high temperatures and acquires characteristics of the Yb3+ LM ESR at low temperature. This dual behavior in same ESR spectra strikes as an in situ unique observation of the Kondo quasiparticles giving rise to a new ESR response called Kondo coupled resonant mode (KCRM). The proximity to a quantum critical point (QCP) may favor the observation of a KCRM and its dual character in beta-YbAlB4 may unveil the 4f-electrons nature at the QCP.