Geometry-Driven Charge and Spin Transport in $\beta12$ Borophene Quantum Dots

TL;DR

This work investigates how confinement geometry (disc vs hexagon) and lead termination (zigzag vs armchair) influence charge and spin transport in finite $\beta_{12}$ borophene quantum dots. Using a five-band tight-binding model calibrated to first-principles data and non-equilibrium Green's function transport, the authors analyze spin-resolved transmissions under a proximity-induced exchange field $M$. They identify lead-width thresholds at about $1.01\ \mathrm{nm}$ (zigzag) and $0.87\ \mathrm{nm}$ (armchair) where zero-transmission regions disappear, and show armchair contacts yield broader, more robust fully spin-polarized windows for both disc and hexagon geometries. The central-radius has limited effect compared with lead-edge confinement, underscoring the importance of edge termination in designing borophene-based spintronic devices and providing actionable guidelines for energy-selective spin filtering via geometry and exchange coupling.

Abstract

Theoretical research has been conducted to study how geometry affects charge and spin transport in $β\mathrm{12}$ borophene quantum dots, which are confined systems. The study examined two distinct central regions, which included a circular disc and a regular hexagonal area that connected to semi-infinite zigzag and armchair borophene nanoribbon leads. The system was described by a five-band tight-binding Hamiltonian parameterized using first-principles data, and the transport properties were calculated within the non-equilibrium Green's function framework. Spin resolved transmissions and spin polarization were computed for a range of lead widths and proximity-induced exchange field strengths. The analysis revealed distinct transport characteristics determined by geometry and edge configuration: armchair-connected structures exhibited broader and more stable fully spin-polarized windows compared with zigzag-connected counterparts. Furthermore, critical lead-width thresholds ($\approx 1.01$ nm for zigzag and $\approx 0.87$ nm for armchair) and a moderate exchange field above which complete spin filtering occurs were identified. The results highlight the strong influence of edge termination and confinement geometry on transport properties and provide useful design guidelines for developing borophene-based nanoscale spintronic devices.

Figures (11)

• Figure 1: Schematic illustration of the studied structures: disc geometries with (a) zigzag and (b) armchair edge orientations, and hexagonal geometries with (c) zigzag and (d) armchair edge orientations. The unit cell of $\beta_{12}$ borophene is shown on the left side of the figure for reference.
• Figure 2: Band structure (left ) and charge transmission (right ) for borophene nanodisc systems with edge orientations of (a) zigzag and (b) armchair.
• Figure 3: Transmission of initial desired disc with zigzag edges (upper row) and armchair edges (bottom row) by changing leads width (a, c) and disc radius (b, d). Red color indicate zero transmission.
• Figure 4: Minimum transmission (red color) per vary range of lead width and disc radius with zigzag (a) and armchair (b) edges. white zone are related to those leads and disc size where has mismatch in simulations.
• Figure 5: Band structure (left ) and spin-resolved transmission (right ) for borophene nanodisc systems with edge orientations of (a) zigzag and (b) armchair.