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Although topological photonics has been an active field of research for some time, most studies still focus on the linear optical regime. This Perspective summarizes recent investigations into the nonlinear properties of discrete topological photonic systems.
Photoemission experiments demonstrate that the photon number statistics of the exciting light can be imprinted on the emitted electrons, allowing the controlled generation of classical or non-classical electron number statistics of free electrons.
The shape and trajectory of a crack plays a crucial role in material fracture. High-precision experiments now directly capture this phenomenon, unveiling the intricate 3D nature of cracks.
The occurrence of propagating spiral waves in multicellular organisms is associated with key biological functions. Now this type of wave has also been observed in dense bacterial populations, probably resulting from non-reciprocal cell–cell interactions.
Leggett modes can occur when superconductivity arises in more than one band in a material and represent oscillation of the relative phases of the two superconducting condensates. Now, this mode is observed in Cd3As2, a Dirac semimetal.
The ferromagnet CrVI6 serves as a material platform to demonstrate the topological Kerr effect in two-dimensional magnets. This can be used to identify skyrmions by magneto-optical means.
Topological magnetic spin structures such as skyrmions and merons have the potential to be used in magnetic information devices. Now multistep transformations between such structures are demonstrated in a centrosymmetric material.
Despite their potential device applications, experimental realizations of proximity-induced Fulde–Ferrell–Larkin–Ovchinnikov states are rare. Now Josephson junctions based on a dilute magnetic topological insulator provide evidence of such a state.
Even by shining classical light on a single opening, one can perform a double-slit experiment and discover a surprising variety of quantum mechanical multi-photon correlations — thanks to surface plasmon polaritons and photon-number-resolving detectors.
Two adjacent layers flowing at different velocities in the same fluid are subject to flow instabilities. This phenomenon is now studied in atomic superfluids, revealing that quantized vortices act as both sources and probes of the unstable flow.
Interactions of atmospheric neutrinos with quantum-gravity-induced fluctuations of the metric of spacetime would lead to decoherence. The IceCube Collaboration constrains such interactions with atmospheric neutrinos.
Experiments probing three-dimensional crack propagation show that the critical strain energy needed to drive a crack is directly proportional to its geodesic length. This insight is a step towards a fully three-dimensional theory of crack propagation.
Stable regions in four-dimensional phase space have been observed by following the motion of accelerated proton beams subject to nonlinear forces. This provides insights into the physics of dynamical systems and may lead to improved accelerator designs.
Nonlinear resonances can cause particle loss in accelerators. Experiments confirm that a coupled nonlinear resonance traps beam particles on a four-dimensional closed curve. This finding allows the development of mitigation strategies.
A mechanism for the phase transition of charge density wave states via the generation and proliferation of topological defects with opposite phase windings is demonstrated in a heavy-fermion superconductor.
Exploring and exploiting electric dipole arrangements analogously to what is possible with magnetic spin textures is an emerging prospect. Now a spontaneous toroidal polar topology is observed in ferroelectric liquid crystals.
