Conductance of a quantum point contact based on spin-density-functional theory

Abstract

We present full quantum mechanical conductance calculations of a quantum point contact (QPC) performed in the framework of the density functional theory (DFT) in the local spin-density approximation (LDA). We show that a spin-degeneracy of the conductance channels is lifted and the total conductance exhibits a broad plateau-like feature at 0.5*2e^{2}/h. The lifting of the spin-degeneracy is a generic feature of all studied QPC structures (both very short and very long ones; with the lengths in the range 40<l<500 nm). The calculated conductance also shows a hysteresis for forward- and backward sweeps of the gate voltage. These features in the conductance can be traced to the formation of weakly coupled quasi-bound states (magnetic impurities) inside the QPC (also predicted in previous DFT-based studies). A comparison of obtained results with the experimental data shows however, that while the spin-DFT based "first-principle" calculations exhibits the spin polarization in the QPC, the calculated conductance clearly does not reproduce the 0.7 anomaly observed in almost all QPCs of various geometries. We critically examine major features of the standard DFT-based approach to the conductance calculations and argue that its inability to reproduce the 0.7 anomaly might be related to the infamous derivative discontinuity problem of the DFT leading to spurious self-interaction errors not corrected in the standard LDA. Our results indicate that the formation of the magnetic impurities in the QPC might be an artefact of the LDA when localization of charge is expected to occur. We thus argue that an accurate description of the QPC structure would require approaches that go beyond the standard DFT+LDA schemes.

9 pages, 5 figures

References in corpus (8)

• Magnetic impurity formation in quantum point contacts
• Tunneling through nanosystems: Combining broadening with many-particle states
• Coulomb blockade in electron transport through a C${}_{60}$ molecule from first principles
• Testing of two-dimensional local approximations in the current-spin and spin-density-functional theories
• Quantum kinetic description of Coulomb effects in one-dimensional nano-transistors
• Anomalous spin-dependent behaviour of one-dimensional subbands
• Quantum point contact with large localized spin: fractional quantization of the ballistic conductance
• Hysteresis and spin phase transitions in quantum wires in the integer quantum Hall regime

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• Spin polarization in modulation-doped GaAs quantum wires
• Magnetoconductance of interacting electrons in quantum wires: Spin density functional theory study
• Dephasing in a quantum dot coupled to a quantum point contact