Chiral edge transport along domain walls in magnetic topological insulator nanoribbons

TL;DR

This study explores how magnetic domain walls in topological insulator nanoribbons influence chiral edge transport, revealing conditions for conductance quantization and spin polarization, with implications for spin-filter device applications.

Contribution

It provides a detailed analysis of quantum transport in magnetic topological insulator nanoribbons with domain walls, highlighting the impact of domain wall orientation on conductance and spin polarization.

Findings

Conductance quantization occurs with horizontal domain walls.

Perpendicular domain walls do not exhibit conductance quantization.

Edge states are spin polarized in the horizontal domain wall configuration.

Abstract

Quantum anomalous Hall insulators are topologically characterized by non-zero integer Chern numbers, the sign of which depends on the direction of the exchange field that breaks time-reversal symmetry. This feature allows the manipulation of the conducting chiral edge states present at the interface of two magnetic domains with opposite magnetization and opposite Chern numbers. Motivated by this broad understanding, the present study investigates the quantum transport properties of a magnetized $Bi_2Se_3$ topological insulator nanoribbon with a domain wall oriented either parallel or perpendicular to the transport direction. Employing an atomistic tight-binding model and a non-equilibrium Green's function formalism, we calculate the quantum conductance and explore the nature of the edge states. We elucidate the conditions leading to exact conductance quantization and identify the origin of deviations from this behavior. Our analysis shows that although the conductance is quantized in the presence of the horizontal domain wall, the quantization is absent in the perpendicular domain wall case. Furthermore, the investigation of the spin character of the edge modes confirms that the conductance in the horizontal domain wall configuration is spin polarized. This finding underscores the potential of our system as a simple three dimensional spin-filter device.