In a groundbreaking theoretical investigation, researchers have uncovered remarkable properties in the quantum transport behavior of exotic particles known as Floquet Majorana Fermions (FMFs). These elusive quantum entities, when formed at the boundaries of periodically driven topological superconductors, create distinctive signatures in the Josephson current flowing across weakly linked junctions. Floquet Majorana fermions can exist in distinct states not possible without the periodic drive, changing based on their interaction with the cycling energy source. The periodic driving of the superconductor is key to maintaining the FMFs and the unusual patterns they create.
The team, led by Professor Babak Seradjeh, developed analytical formulas that capture how these Floquet Majorana fermions behave when weakly coupled to thermal reservoirs. Their findings reveal a striking similarity to undriven systems: when temperatures are sufficiently low and the system size large enough, the Josephson current exhibits a 4π-periodicity in the phase difference across the junction, while scaling linearly with the coupling strength between the superconductors.
However, the periodically driven systems introduce a fascinating new dimension not present in static configurations. Researchers discovered that the Josephson current’s amplitude can be precisely tuned by aligning the unbiased chemical potential of the driven superconductors with multiple harmonics of the driving frequency. This phenomenon gives rise to what the authors have dubbed a “Josephson Floquet sum rule” – a novel principle governing the behavior of driven superconducting systems.
The theoretical framework constructed by the team stands on solid ground, with their analytical expressions for the Josephson current, Floquet band occupation, and quasienergy analysis rigorously validated against numerically exact calculations.
This research demonstrates a new level of control over quantum materials, paving the way for more stable and efficient quantum computers.
Reference: “Josephson-Current Signatures of Unpaired Floquet Majorana Fermions” by Rekha Kumari, Babak Seradjeh and Arijit Kundu, 6 November 2024, Physical Review Letters. DOI: 10.1103/PhysRevLett.133.196601
