Combining topology and superconductivity provides a powerful tool for investigating fundamental physics as well as a route to fault-tolerant quantum computing. There is mounting evidence that the Fe-Based superconductor FeTe 0.55 Se 0.45 (FTS) may also be topologically non-trivial. Should the superconducting order be s ± , then FTS could be a higher order topological superconductor with Helical Hinge Zero Modes (HHZM).To test the presence of these modes we've fabricated normal-metal/superconductor junctions on different surfaces via 2D atomic crystal heterostructures. As expected, junctions in contact with the hinge reveal a sharp zero-bias anomaly that is absent when tunneling purely into the c-axis. Additionally, the shape and suppression with temperature are consistent with highly coherent modes along the hinge and are incongruous with other origins of zero bias anomalies. Furthermore, additional measurements with soft-point contacts in bulk samples with various Fe interstitial contents demonstrate the intrinsic nature of the observed mode. Thus we provide evidence that FTS is indeed a higher order topological superconductor.ASSOCIATED CONTENT: Supporting information available. Supporting information includes details regarding: exfoliation and fabrication of devices, experimental measurement setup, additional crystal measurements, and additional controls and checks performed on the devices.

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Theory–experiment advancements are demonstrated to resolve many-body correlations of quantum materials at attosecond time scales. Our theoretical analysis provides an exact view into the microscopic many-body dynamics presented intuitively via a Wigner-function analysis.

We demonstrate an active carrier-envelope phase (CEP) stabilization scheme for optical waveforms generated by difference-frequency mixing of two spectrally detuned and phase-correlated pulses. By performing ellipsometry with spectrally overlapping parts of two co-propagating near-infrared generation pulse trains, we stabilize their relative timing to 18 as. Consequently, we can lock the CEP of the generated mid-infrared (MIR) pulses with a remaining phase jitter below 30 mrad. To validate this technique, we employ these MIR pulses for high-harmonic generation in a bulk semiconductor. Our compact, low-cost, and inherently drift-free concept could bring long-term CEP stability to the broad class of passively phase-locked OPA and OPCPA systems operating in a wide range of spectral windows, pulse energies, and repetition rates.