Engineering topics
Hunt, Benjamin M.
Publications and source records attributed to Hunt, Benjamin M..
Quantum Spin Hall Edge States and Interlayer Coupling in Twisted Bilayer WTe 2
The quantum spin Hall (QSH) effect, characterized by topologically protected spin-polarized edge states, was recently demonstrated in monolayers of the transition metal dichalcogenide (TMD) WTe 2 . However, the robustness of this topological protection remains largely unexplored in van der Waals heterostructures containing one or more layers of a QSH insulator. Here, we use scanning tunneling microscopy and spectroscopy (STM/STS) to explore the topological nature of twisted bilayer (tBL) WTe 2 . Furthermore, at the tBL edges, we observe the characteristic spectroscopic signatures of the QSH edge states. For small twist angles, a rectangular moiré pattern develops, which results in local modifications of the band structure. Using first-principles calculations, we quantify the interactions in tBL WTe 2 and its topological edge states as a function of interlayer distance and conclude that it is possible to engineer the topology of WTe 2 bilayers via the twist angle as well as interlayer interactions.
Superconducting contact and quantum interference between two-dimensional van der Waals and three-dimensional conventional superconductors
Atomically thin two-dimensional (2D) transition-metal dichalcogenide (TMD) superconductors enable uniform, flat, and clean van der Waals tunneling interfaces, motivating their integration into conventional superconducting circuits. However, fully superconducting contact must be made between the 2D material and three-dimensional (3D) superconductors to employ the standard microwave drive and readout of qubits in such circuits. We present a method for creating zero-resistance contacts between 2D NbSe 2 and 3D aluminum that behave as Josephson junctions (JJs) with large effective areas compared to 3D-3D JJs. The devices formed from 2D TMD superconductors are strongly influenced by the geometry of the flakes themselves as well as the placement of the contacts to bulk 3D superconducting leads. We present a model for the supercurrent flow in a 2D-3D superconducting structure by a numerical solution of the Ginzburg-Landau equations and find good agreement with experiment. Finally, these results demonstrate a crucial step towards a new generation of hybrid superconducting quantum circuits.
Proximity-induced superconducting gap in the quantum spin Hall edge state of monolayer WTe2
The quantum spin Hall insulator is characterized by a bandgap in the two-dimensional (2D) interior and helical 1D edge states 1 , 2 , 3 . Inducing superconductivity in the helical edge state results in a 1D topological superconductor, a highly sought-after state of matter at the core of many proposals for topological quantum computing 4 . In the present study, we report the coexistence of superconductivity and the quantum spin Hall edge state in a van der Waals heterostructure, by placing a monolayer of 1T'-WTe 2 , a quantum spin Hall insulator 1 , 2 , 3 , on a van der Waals superconductor, NbSe 2 . Using scanning tunnelling microscopy and spectroscopy (STM/STS), we demonstrate that the WTe 2 monolayer exhibits a proximity-induced superconducting gap due to the underlying superconductor and that the spectroscopic features of the quantum spin Hall edge state remain intact. Taken together, these observations provide conclusive evidence for proximity-induced superconductivity in the quantum spin Hall edge state in WTe 2 , a crucial step towards realizing 1D topological superconductivity and Majorana bound states in this van der Waals material platform.