Magnetotransport signatures of three-dimensional topological insulator nanostructures

Abstract

We study the magnetotransport properties of patterned 3D topological insulator nanostructures with several leads, such as kinks or Y-junctions, near the Dirac point with analytical as well as numerical techniques. The interplay of the nanostructure geometry, the external magnetic field and the spin-momentum locking of the topological surface states lead to a richer magnetoconductance phenomenology as compared to straight nanowires. Similar to straight wires, a quantized conductance with perfect transmission across the nanostructure can be realized across a kink when the input and output channels are pierced by a half-integer magnetic flux quantum. Unlike for straight wires, there is an additional requirement depending on the orientation of the external magnetic field. A right-angle kink shows a unique π-periodic magnetoconductance signature as a function of the in-plane angle of the magnetic field. For a Y-junction, the transmission can be perfectly steered to either of the two possible output legs by a proper alignment of the external magnetic field. These magnetotransport signatures offer new ways to explore topological surface states and could be relevant for quantum transport experiments on nanostructures which can be realized with existing fabrication methods.

Reappearance of first Shapiro step in narrow topological Josephson junctions

“…We now focus on the investigation of junctions on narrow BST nanoribbons of only W = 200 nm that have been defined using a SAG approach ( 24 , 36 , 37 ). In Josephson junctions on selectively deposited nanoribbons, the geometry of the junction is defined by the width W of the TI nanoribbon and the electrode separation L of the two superconducting electrodes.…”

“…In addition, we explore the behavior of junctions with reduced width of the BST weak link. TI nanoribbons that are only 200 nm wide are deposited using a selective area growth (SAG) approach (23,24). In nanoribbon geometries, transverse momentum states are quantized due to the confinement of surface charges on the nanoribbon perimeter P. The quantization leads to a bandgap opening within the Dirac surface states, which become spin degenerate (25)(26)(27)(28).…”

Proximity‐Effect‐Induced Superconductivity in Nb/Sb2Te3‐Nanoribbon/Nb Junctions

“…the propagation direction of surface electrons is robustly locked to the spin orientation. [ 4–7 ] Among the 3D TIs mentioned above, Sb 2 Te 3 is particularly interesting since it comprises a relatively large bulk band gap of about 200 meV and a Dirac point within the gap. [ 1,8 ] Regarding phenomena at low temperatures Zhang et al .…”

Crossed Andreev reflection in topological insulator nanowire T junctions

“…This is of relevance, as we want to have a flux of φ = φ 0 /2 penetrating the NS-interface. The penetration depth of the surface states defines an effective cross section area and therefore it is necessary to rescale the field strength [42]. In App.…”