Scanning gate microscopy mapping of edge current and branched electron flow in a transition metal dichalcogenide nanoribbon and quantum point contact

TL;DR

This study uses scanning gate microscopy to map edge and branched electron flow in MoS2 nanoribbons and quantum point contacts, revealing details about edge modes, spin-valley currents, and effects of disorder.

Contribution

It demonstrates how conductance mapping can identify edge modes, spin-orbit effects, and valley mixing in transition metal dichalcogenide nanostructures.

Findings

Edge modes are robust to tip-induced backscattering.

Conductance mapping reveals spin and valley current modes.

Disorder induces valley mixing and fringe beating patterns.

Abstract

We study scanning gate microscopy (SGM) conductance mapping of a $\mathrm{MoS}_2$ zigzag ribbon exploiting tight-binding and continuum models. We show that, even though the edge modes of a pristine nanoribbon are robust to backscattering on the potential induced by the tip, the conductance mapping reveals presence of both the edge modes and the quantized spin- and valley-current carrying modes. By inspecting the electron flow from a split gate quantum point contact (QPC) we find that the mapped current flow allows to determine the nature of the quantization in the QPC as spin-orbit coupling strength affects the number of branches in which the current exits the constriction. The radial conductance oscillation fringes found in the conductance mapping reveal the presence of two possible wavevectors for the charge carriers that correspond to spin and valley opposite modes. Finally, we show that disorder induced valley mixing leads to a beating pattern in the radial fringes.