Quantum Criticality in Ferromagnetic Single-Electron Transistors

TL;DR

This paper proposes using ferromagnetic single-electron transistors as a model system to study quantum criticality, revealing a gate-induced quantum phase transition and fractional power-law behaviors in conductance and noise spectra.

Contribution

It introduces a theoretical framework demonstrating a quantum phase transition in ferromagnetic transistors and links the critical Kondo effect to observable power-law dependencies.

Findings

Gate-voltage induces quantum phase transition.

Conductance shows fractional-power-law dependence on temperature.

AC conductance and noise spectra exhibit $\omega/T$ scaling.

Abstract

Considerable evidence exists for the failure of the traditional theory of quantum critical points (QCPs), pointing to the need to incorporate novel excitations. The destruction of Kondo entanglement and the concomitant critical Kondo effect may underlie these emergent excitations in heavy fermion metals -- a prototype system for quantum criticality -- but the effect remains poorly understood. Here, we show how ferromagnetic single-electron transistors can be used to study this effect. We theoretically demonstrate a gate-voltage induced quantum phase transition. The critical Kondo effect is manifested in a fractional-power-law dependence of the conductance on temperature ($T$). The AC conductance and thermal noise spectrum have related power-law dependences on frequency ($\omega$) and, in addition, show an $\omega/T$ scaling. Our results imply that the ferromagnetic nanostructure constitutes a realistic model system to elucidate magnetic quantum criticality that is central to the heavy fermions and other bulk materials with non-Fermi liquid behavior.