Magnetic Single-Electron Transistor as a Tunable Model System for Kondo-Destroying Quantum Criticality

TL;DR

This paper investigates a magnetic single-electron transistor as a tunable system to explore Kondo-destroying quantum criticality, revealing insights into non-Fermi liquid behavior and critical destruction of the Kondo effect.

Contribution

It models the quantum critical point using an effective Bose-Fermi Kondo model with sub-Ohmic dissipation, extending understanding of Kondo destruction in quantum phase transitions.

Findings

Identification of a continuous quantum phase transition in the system.

Analysis of transport properties near the quantum critical point.

Discussion of the effects of different dissipative baths and magnetic fields.

Abstract

Single-electron transistors attached to ferromagnetic leads can undergo a continuous quantum phase transition as their gate voltage is tuned. The corresponding quantum critical point separates a Fermi liquid phase from a non-Fermi liquid one. Here, we expound on the physical idea proposed earlier. The key physics is the critical destruction of the Kondo effect, which underlies a new class of quantum criticality that has been argued to apply to heavy fermion metals. Its manifestation in the transport properties is studied through an effective Bose-Fermi Kondo model; the bosonic bath, corresponding to the spin waves of the ferromagnetic leads, describes a particular type of sub-Ohmic dissipation. We also present results for general forms of sub-Ohmic dissipative bath, and consider in some detail the case with critical paramagons replacing spin waves. Finally, we discuss some delicate aspects in the theoretical treatment of the effect of a local magnetic field, particularly in connection with the frequently employed Non-Crossing Approximation.