ABSTRACT
Direct detection of spontaneous spin fluctuations, or "magnetization noise," is emerging as a powerful means of revealing and studying magnetic excitations in both natural and artificial frustrated magnets. Depending on the lattice and nature of the frustration, these excitations can often be described as fractionalized quasiparticles possessing an effective magnetic charge. Here, by combining ultrasensitive optical detection of thermodynamic magnetization noise with Monte Carlo simulations, we reveal emergent regimes of magnetic excitations in artificial "tetris ice." A marked increase of the intrinsic noise at certain applied magnetic fields heralds the spontaneous proliferation of fractionalized excitations, which can diffuse independently, without cost in energy, along specific quasi-1D spin chains in the tetris ice lattice.
ABSTRACT
One-dimensional strings of local excitations are a fascinating feature of the physical behavior of strongly correlated topological quantum matter. Here we study strings of local excitations in a classical system of interacting nanomagnets, the Santa Fe Ice geometry of artificial spin ice. We measured the moment configuration of the nanomagnets, both after annealing near the ferromagnetic Curie point and in a thermally dynamic state. While the Santa Fe Ice lattice structure is complex, we demonstrate that its disordered magnetic state is naturally described within a framework of emergent strings. We show experimentally that the string length follows a simple Boltzmann distribution with an energy scale that is associated with the system's magnetic interactions and is consistent with theoretical predictions. The results demonstrate that string descriptions and associated topological characteristics are not unique to quantum models but can also provide a simplifying description of complex classical systems with non-trivial frustration.
ABSTRACT
Plasmonic effects have proven to be very efficient in coupling light to structures much smaller than its wavelength. Efficient coupling is particularly important for the infrared or terahertz (λ â¼ 0.3 mm) region where semiconductor structures and devices may be orders of magnitude smaller than the wavelength and this can be achieved through nanostructures that have a desired plasmonic response. We report and demonstrate a self-assembly method of embedding controllable semimetallic nanostructures in a semiconducting matrix in a ErSb/GaSb material system grown by molecular beam epitaxy. The plasmonic properties of the ErSb/GaSb are characterized and quantified by three polarization-resolved spectroscopy techniques, spanning more than 3 orders of magnitude in frequency from 100 GHz up to 300 THz. Surface plasmons cause the semimetallic nanostructures to resonate near 100 THz (3 µm wavelength), indicating the semimetal as a potential infrared plasmonic material. The highly conductive ErSb nanowires polarize electromagnetic radiation in a broad range from 0.2 up to â¼100 THz, providing a new platform for electromagnetics in the infrared and terahertz frequency ranges.
