Edge Channel Transmission through a Quantum Point Contact in the Two-Dimensional Topological Insulator Cadmium Arsenide

Abstract

Cadmium arsenide (Cd 3 As 2 ) thin films feature a two-dimensional topological insulator (2D TI) phase for certain thicknesses, which theoretically hosts a set of counterpropagating helical edge statesA bar has been added to each symbol of the high-symmetry points of Cu(100) and Cu(111). The bar indicates the surface projected Brillouin zone. that are characteristic of a quantum spin Hall (QSH) insulator. In devices containing electrostatically defined junctions and for magnetic fields below a critical value, chiral edge modes of the quantum Hall effect can coexist with QSH-like edge modes. In this work, we use a quantum point contact (QPC) device to characterize edge modes in the 2D TI phase of Cd 3 As 2 and to understand how they can be controllably transmitted, which is important for use in future quantum interference devices. We investigate equilibration among both types of modes and find non-spin-selective equilibration. We also demonstrate the effect of the magnetic field on suppressing equilibration. We discuss the potential role of QSH-like modes in a transmission pathway that precludes full pinch-off.

Shot Noise in Helical Edge States in Presence of a Static Magnetic Defect

“…Although this model of the contact is very simplified, it is commonly used in the quantum interferometry, starting from the work [38], since it allows one to describe the transition from the metal contact (t = 0) to the tunnel contact (t = 1). In particular, this model qualitatively describes quantum point contacts to the HES, which have already been used in the recent experiment [33].…”

“…Moreover, for any contacts, with the exception of purely metallic ones (for example, for tunnel contacts or quantum point contacts), there is a finite probability of passing by the contact without leaving the sample, i.e., both "right-handed" and "left-handed" electrons can wind around the sample several times before coming out to the contact, and the corresponding processes can interfere. Note that quantum point contacts to the HES have already been realized experimentally [33], so that possible manifestations of interference effects in conductance and noise allow experimental verification, especially having in mind that condition does not require very strict restrictions on temperature.…”