Spin splitting in open quantum dots

Abstract

We demonstrate that the magnetoconductance of small lateral quantum dots in the stronglycoupled regime (i.e. when the leads can support one or more propagating modes) shows a pronounced splitting of the conductance peaks and dips which persists over a wide range of magnetic fields (from zero field to the edge-state regime) and is virtually independent of the magnetic field strength. Our numerical analysis of the conductance based on the Hubbard Hamiltonian demonstrates that this is essentially a many-body/spin effect that can be traced to a splitting of degenerate levels in the corresponding closed dot. The above effect in open dots can be regarded as a counterpart of the Coulomb blockade effect in weakly coupled dots, with the difference, however, that the splitting of the peaks originates from the interaction between the electrons of opposite spin.

Spin polarization in open quantum dots

“…[7] had relatively large electron density (n s ∼ 2 × 10 15 m −2 ), whereas the dots in Ref. [9] had low electron density, (n s < 7×10 14 m −2 ), such that the observed features [7,9] are consistent with our findings that spin polarization diminishes as the electron density in the dot increases.…”

“…At the same time, the results of Ref. [9] suggested that the spin degeneracy in open dots is lifted. Our findings reported above seem to reconcile these apparently different experimental observations.…”

“…The similar conclusion follows from the results of Folk et al [8] who experimentally demonstrated the operation of an open dot as a spin filter. In contrast, low-field magnetoconductance of small dots [9] showed a pronounced peak splitting that was taken as a signature of the spin polarization. In contrast to QPCs, where theoretical investigations of the spin polarization have been a subject of lively discussions during recent years [10,11,12,13,14,15], theoretical description of spin-polarization effects in open quantum dots has received far less attention.…”

“…In our previous work [9], we investigated transport in similar dots using the mean-field Hubbard hamiltonian, H σ = H 0 + U n ↑ (r)n ↓ (r), where on-site Hubbard constant U describes the Coulomb interaction between electrons of opposite spins. Within this model we found that spin polarization in the dot takes place only when the Fermi energy hits the resonant states weakly coupled to the leads.…”

Spin polarization in modulation-dopedGaAsquantum wires

“…The phenomena has been suggested to occur in various systems including quantum point contacts 1 ͑QPCs͒, two-dimensional electron gas ͑2DEG͒, 2,3 quantum wire, 4 and open quantum dots. 5 Theoretical modeling with Hartree-Fock, 6 the density functional theory, 5,[7][8][9] and Monte Carlo simulations 10 has reproduced low density spin polarization in a number of systems. The mechanism driving the polarization is the exchange energy dominating over the kinetic energy at low densities, making the spin-polarized state the energetically most favorable.…”