Topological Superconductivity Enables Low-Energy, Error-Free Spintronic Devices.

The pursuit of topological superconductivity, a state of matter predicted to host robust, dissipationless electronic states at its boundaries, promises advances in spintronics and quantum computing. Identifying unambiguous experimental evidence of these states, however, remains a significant challenge. Wenyao Liu, Gabriel Natale, and colleagues report the first observation of protected, non-local transport mediated by edge modes in the iron-based compound. Their findings, detailed in the article “Weyl-Superconductivity revealed by Edge Mode mediated Nonlocal Transport”, demonstrate a novel methodology for confirming the existence of topological superconductivity through the observation of ballistic charge transport along topologically protected edge states, a process distinctly different from conventional electrical conduction. The research involved a collaborative effort spanning Boston College, the University of California, Irvine, Boston University, and the National Institute of Standards and Technology.

The pursuit of topological superconductivity receives considerable impetus as researchers present definitive evidence of its existence within the iron-based superconductor FeTe₀.₅₅Se₀.₄₅, revealing protected, non-local transport originating from edge modes and solidifying its potential for advanced spintronic devices. Topological superconductivity is a state of matter exhibiting conventional superconductivity alongside topological properties, meaning it possesses robust surface states protected from disorder. This latest work achieves a breakthrough through resonant charge injection and extraction via these edge modes, confirming ballistic transport – where electrons travel without scattering – along them and establishing a new methodology for identifying topological superconductivity edge states.

Researchers consistently observe these edge modes using gate-modulated differential conductance, a technique measuring the change in electrical current with applied voltage and gate voltage, gate-modulated scanning tunnelling spectroscopy, which probes the local electronic structure, and conventional scanning tunnelling spectroscopy. These observations reveal the sensitivity of the edge modes to external stimuli and establish a connection to the material’s inherent properties. The observed zero-bias conductance peak, a signature of superconductivity appearing at zero voltage, persists up to a critical temperature, confirming its connection to the superconducting state and providing a clear signature of the material’s superconducting behaviour.

The study identifies a unique conductance plateau that emerges only when topological, superconducting, and magnetic phases coexist within the material, providing a specific parameter space for observing and controlling these exotic states. Crucially, coupling source and drain contacts via these edges facilitates this non-local transport, enabling the observation of these unique phenomena and providing a clear pathway for future research. When the drain contact is moved to the bulk of the material, the transport mechanism switches to a local Andreev reflection process – where an electron and a hole are created at an interface – resulting in a zero-bias conductance peak, providing a clear contrast and confirming the edge-specific nature of the observed phenomena.

Furthermore, the study demonstrates the topological protection of these edge modes, as they remain largely unaffected by increasing temperatures or applied magnetic fields until the material’s spontaneous magnetisation is substantially reduced, highlighting their robustness and potential for practical applications. The robustness of the zero-bias conductance peak to variations in temperature and applied magnetic fields provides strong support for the topological protection of these edge states, solidifying their potential for use in robust quantum computing and spintronics, a field exploiting electron spin for information processing.

Correlation between the temperature dependence of the zero-bias conductance peak width and the polar Kerr effect – a change in the polarisation of reflected light due to magnetism – establishes a link between the edge states and the bulk superconducting properties, providing valuable insights into the underlying mechanisms governing superconductivity within the material. This connection suggests a complex interplay between the topological edge states and the superconducting state within the bulk material, furthering understanding of this novel state of matter.