EAGER: BRAIDING: Majorana modes in monolayer topological insulator WTe2

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Nontechnical Abstract: Finding alternative paths to quantum computing is paramount at this time, and current approaches face many hurdles. The biggest is decoherence of the qubits, meaning that the quantum information content decays exponentially with time. In principle, decoherence can be avoided using "topological protection". The only realistic known scheme for topological protection is based on creating the qubits from so-called Majorana modes, which are peculiar states that occur at the ends of certain types of quantum wires. One way to make Majoranas is using the special quantum wire that exists at the edge of a topological insulator. The PI, an experimentalist, recently discovered the first natural monolayer two-dimensional (2D) topological insulator, suggesting the possibility to create and manipulate Majoranas in 2D materials. The co-PI is a theorist and expert on topological phenomena; in this project they collaborate to find the simplest way to create and detect Majoranas in this system. The work supports graduate students in topical interdisciplinary work where theory and experiment go hand in hand, and which could conceivably give birth to the next information revolution. The project forms a bridge between the University of Washington, which has a leading research effort in 2D materials, and local industry (including Microsoft) which is investing heavily in applications of quantum computers.Technical: This project aims to establish the viability of the 2D materials platform for creating Majorana zero modes that could be used for topological quantum processing. The team employs monolayer WTe2 as a 2D topological insulator, combined with a 2D superconductor (NbSe2 or FeSe) and a 2D magnet (CrI3 or CrBr3). These materials are stacked into a van der Waals heterostructure along with electrical contacts and tunnel barriers. At the point where the three materials meet a Majorana mode may appear at low temperatures and can be probed by tunneling measurements. This 2D platform offers advantages compared with other Majorana systems including that no magnetic field is required to produce the helical mode, and the possibility to avoid delicate tuning of the chemical potential. The complexity of the many-electron and topological physics involved, and the novelty of the system, calls for close cooperation between experiment and theory. Specific goals are to induce and understand a superconducting proximity gap in the helical edge of WTe2, and to design and test the simplest 2D possible heterostructure devices in which Majoranas may occur and be detected.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.