Kondo resonance effects in emergent flat band materials

Abstract

Macroscopic degrees of freedom that are involved in the transport of carriers through mesoscopic electronic devices are susceptible to the effects of strong many-body correlations. The presence of magnetic impurities in dilute magnetic alloys typically allow for insights into Kondo effect from the scattering of free carriers by localized electron states of the magnetic impurities but this effect is not well understood when there are no d-band electron states. Herein, the signatures of Kondo resonance effect are elucidated in quantum dots derived from a carbon-nanoline embedded monolayer hexagonal boron nitride whose electron states host flat band ferromagnetism as distinct broken symmetry states. Quantum transport state of mesoscopic devices modelled as quantum dots tunnel coupled to metallic leads is computed by direct diagonalization of the Hamiltonian. The possibility of realizing quantum dots with highly tunable electron states in energy interconversion devices is discussed to show the importance of screening effects on single-electron energy levels. The quantum master equation is solved within different formalisms to determine the stationary-state particle and energy currents. Stability diagrams are calculated to show the dependence of the conductance on experimental control variables of the quantum dot device. The computed responses of the stationary-state transport signatures are used to characterize Kondo resonance effects from flat band states of embedded carbon nanoline-based quantum dots. It is found that the local network structure of the hexagonal ring carbon cluster-based quantum dot has a broken particle-hole symmetry in the transport state. This signals the formation of the quasiparticle states expected in second order scattering when the macroscopic “charge” pseudospin symmetry of the tunnelling electron state is broken dynamically due to charging. The results are discussed to show the implications of a vanishing particle-hole symmetry in the carrier transport state of quantum dots for energy conversion applications.

Unveiling the emergence of topological quantum phase transitions in the bidirectional transport of carriers through helical edge states in bismuth selenide

“…An imposed TRS causes the full polarisation of the charge pseudospin-½ degree of freedom at the KK'-points of the BZ even though the SOC is small in monolayer hBN (see Figs 4(a) and (b) in Ref. [8]). By comparison, Fig.…”

“…Phenomenological fields were applied to the renormalized graphene ribbons to perturb the electronic structure and break the intrinsic symmetry of the ground state. This computational strategy allows the emergence of topological phases to be understood by systematically studying ways to open a band gap by either preserving or breaking symmetries in the electronic structure of the renormalized graphene [29,30] without interference from proximity-enhancements of the SOC by the substrate in a bilayer system [31], thus preserving the particle-hole symmetry of the electron-hole states [8]. The field effects studied here include contributions from intrinsic SOC, Haldane coupling (i.e., a complex second nearest neighbour hopping), and the sublattice imbalance 𝜇 using tunable parameters in the Hamiltonian the system, which is expressed as a sum of terms: 𝐻 = 𝐻 0 + 𝐻 SOC + 𝐻 HC + 𝐻 𝜇 .…”

“…Effective paths for efficient carrier transport can be obtained by rational design. For example, they are obtainable when a thin array of highly conductive species is by embedded in a matrix to form nanolines [8] and nanoroads [9], or when a contiguous region of high charge densities spontaneously forms in a non-conducting or poorly conducting medium [10]. The crucial first step towards realising a robust conducting channel that is both resilient to longranged disorder and capable of serving as interconnects for integration in hardware components for building fault-tolerant quantum computers is to gain an underpinning understanding of the nature of the low-dimensional carrier transport channels in a prototypical TI.…”