Noise Detection of Mobile Magnetic Excitations in a Vertex-Frustrated Artificial Spin Ice

Direct detection of equilibrium spin fluctuations, or "magnetization noise", is emerging as a powerful means of revealing and studying topologically-protected magnetic excitations in both natural and artificial frustrated magnets. Depending on the lattice geometry and nature of the frustration, these excitations can often be described as quasiparticles that behave as mobile magnetic charges. Here, using ultrasensitive optical detection of spontaneous magnetization noise in a thermally active system, supported by additional insight from Monte Carlo simulations, we reveal new regimes of mobile magnetic excitations in the vertex-frustrated artificial spin ice lattices, including tetris and Shakti geometries. A substantial increase of the detected noise for specific directions and ranges of applied in-plane magnetic field heralds the proliferation of these excitations, which can diffuse freely, without any cost in energy, along specific quasi-1D paths in the lattice. As such, those magnetic excitations have no analogous counterpart in naturally-occurring materials and constitute an interesting subject in studies of magnetricity.