Kramers polarization in strongly correlated carbon nanotube quantum dots

Abstract

Ferromagnetic contacts put in proximity with carbon nanotubes induce spin and orbital polarizations. These polarizations affect dramatically the Kondo correlations occurring in quantum dots formed in a carbon nanotube, inducing effective fields in both spin and orbital sectors. As a consequence, the carbon nanotube quantum dot spectral density shows a fourfold split SU(4) Kondo resonance. Furthermore, the presence of spin-orbit interactions leads to the occurrence of an additional polarization among time-reversal electronic states (polarization in the time-reversal symmetry or Kramers sector). Here, we estimate the magnitude for the Kramer polarization in realistic carbon nanotube samples and find that its contribution is comparable to the spin and orbital polarizations. The Kramers polarization generates a new type of effective field that affects only the time-reversal electronic states. We report new splittings of the Kondo resonance in the dot spectral density which can be understood only if Kramers polarization is taken into account. Importantly, we predict that the existence of Kramers polarization can be experimentally detected by performing nonlinear differential conductance measurements. We also find that, due to the high symmetry required to build SU(4) Kondo correlations, its restoration by applying an external field is not possible in contrast to the compensated SU(2) Kondo state observed in conventional quantum dots.

Nonequilibrium spin-current detection with a single Kondo impurity

“…[12][13][14][15][16] It has also been successfully evidenced in nanoscale devices, [17][18][19][20][21] in particular quantum dots, [17][18][19][22][23][24] carbon nanotubes, [25][26][27] and nanowires. 28 Of particular interest-especially in the context of spintronics, is the issue of screening in the presence of a magnetic environment such as spin-polarized electrodes [29][30][31][32][33][34][35] and spinpolarized edge states. 36 A spin-dependent hybridization for the spin-up and spin-down energy levels of the impurity is then predicted, resulting in an effective static magnetic field at the impurity site (this field can eventually be compensated by an external magnetic field).…”

Kondo effect in a quantum dot side-coupled to a topological superconductor

“…The Kondo physics can be further modified by utilizing different types of contact materials, say, superconducting [12][13][14] or ferromagnetic ones. [15][16][17][18] In particular, contacted with an s-wave superconductor, the Kondo spin experiences a quantum phase transition from the spin singlet state to the doublet state as the superconducting gap increases over the Kondo temperature T K . 12,13 Recently, topological superconductors (TSs) have attracted a lot of attention because they realize topological phases that support Majorana fermion states (MFSs) at their boundaries and at topological defects.…”

Fano Antiresonance and Kondo Resonance for Electronic Transport Through a Laterally Coupled Carbon-Nanotube Quantum-Dot System

“…In the presence of parallel magnetic fields, the quantum dot level ε jm is [6,30] σ τ ε ε ε στ∆ τµ σ…”