Stability of conductance oscillations in monatomic sodium wires

TL;DR

This study investigates the stability of conductance oscillations in monatomic sodium wires, revealing that odd-numbered wires maintain stable conductance near the quantum unit, while even-numbered wires are more sensitive to structural variations.

Contribution

The paper provides a first-principles analysis of conductance oscillations in sodium wires, demonstrating the robustness of odd-numbered wires and the sensitivity of even-numbered wires to geometric changes.

Findings

Odd-numbered wires have conductance close to G0 and are stable.

Even-numbered wires exhibit lower, more variable conductance.

Conductance oscillations depend on resonance conditions and wire geometry.

Abstract

We study the stability of conductance oscillations in monatomic sodium wires with respect to structural variations. The geometry, the electronic structure and the electronic potential of sodium wires suspended between two sodium electrodes are obtained from self-consistent density functional theory calculations. The conductance is calculated within the framework of the Landauer-B\"utttiker formalism, using the mode-matching technique as formulated recently in a real-space finite-difference scheme [Phys. Rev. B \textbf{70}, 195402 (2004)]. We find a regular even-odd conductance oscillation as a function of the wire length, where wires comprising an odd number of atoms have a conductance close to the quantum unit $G_0=e^2/\pi\hbar$, and even-numbered wires have a lower conductance. The conductance of odd-numbered wires is stable with respect to geometry changes in the wire or in the contacts between the wire and the electrodes; the conductance of even-numbered wires is more sensitive. Geometry changes affect the spacing and widths of the wire resonances. In the case of odd-numbered wires the transmission is on-resonance, and hardly affected by the resonance shapes, whereas for even-numbered wires the transmission is off-resonance and sensitive to the resonance shapes. Predicting the amplitude of the conductance oscillation requires a first-principles calculation based upon a realistic structure of the wire and the leads. A simple tight-binding model is introduced to clarify these results.