Two-channel charge-Kondo physics in graphene quantum dots

TL;DR

This paper theoretically investigates a graphene-based two-channel charge-Kondo device, revealing complex phase behavior, quantum phase transitions, and non-Fermi liquid conductance, thus offering a platform to study multichannel pseudogap Kondo physics.

Contribution

It introduces a pseudogapped two-channel charge-Kondo model in graphene, solving it with NRG and uncovering novel phases and quantum criticality.

Findings

Persistence of strong coupling pseudogap Kondo phase in channel asymmetry

Quantum phase transition in the symmetric case due to frustration

Finite zero-temperature conductance at the critical point despite vanishing density of states

Abstract

Nanoelectronic quantum dot devices exploiting the charge-Kondo paradigm have been established as versatile and accurate analog quantum simulators of fundamental quantum impurity models. In particular, hybrid metal-semiconductor dots connected to two metallic leads realize the two-channel Kondo (2CK) model, in which Kondo screening of the dot charge pseudospin is frustrated. Here, we consider theoretically a two-channel charge-Kondo device made instead from graphene components, realizing a pseudogapped version of the 2CK model. We solve the model using Wilson's Numerical Renormalization Group method, and uncover a rich phase diagram as a function of dot-lead coupling strength, channel asymmetry, and potential scattering. The complex physics of this system is explored through its thermodynamic properties, scattering T-matrix, and experimentally measurable conductance. We find that the strong coupling pseudogap Kondo phase persists in the channel-asymmetric two-channel context, while in the channel-symmetric case frustration results in a novel quantum phase transition. Remarkably, despite the vanishing density of states in the graphene leads at low energies, we find a finite linear conductance at zero temperature at the frustrated critical point, which is of non-Fermi liquid type. Our results suggest that the graphene charge-Kondo platform offers a unique possibility to access multichannel pseudogap Kondo physics.