Understanding the Hinge Modes in a Topological Superconductor

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Non-Technical Abstract:In recent years a new kind of phase of matter has been predicted, called a Higher Order topological state. This state contains specific new modes on intersections of different surfaces of the crystal. These so-called "hinge" or "corner" modes have the potential to form the basis of future topological quantum computers, immune to errors and able to perform calculations currently unthinkable. An exciting example of such materials is FeTeSe, where the PI provided the first evidence that it is a higher order topological superconductor. Using expertise in fabrication, electrical, and optical spectroscopy, the PI will develop new means to probe the properties of the hinge modes in FeTeSe systematically. The topics and techniques also provide an excellent starting point for creating public talks and recruiting a diverse set of trainees, undergraduate and graduate students, who also participate in public outreach. The project's participants gain valuable professional skills in: collaboration, computation, fabrication, and characterization. Technical Abstract:Higher order topological phases have recently emerged, with boundary modes in two or more dimensions smaller than the bulk. These are systems whose boundary states are themselves topological, gapped with different signs. Using his expertise in fabrication, electrical, and optical spectroscopy, the PI will develop new means to probe the properties of the hinge modes in FeTeSe. An array of contact configurations and protocols will determine the best method to isolate the hinge from the bulk. This effort is aided by photothermal measurements to image the hinges. Careful studies of the effects of magnetic fields and magnetic contacts will determine the details of spin momentum locking. The studies will reveal the transport, thermal, and spin-momentum locking of the hinge modes. As such, their robustness will be directly probed, along with determining the proper ground-state Hamiltonian to describe the hinges.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.