Topological Magnetism Group

Abstract:

Full size CCD camera videos for https://www.nature.com/articles/s41467-018-04563-4

Abstract:

Non-collinear spin textures, such as spin spirals and skyrmions, exhibit rich emergent physics in their spin dynamics. Nevertheless, the potential to utilize their distinctive spin resonance characteristics for on-chip microwave magnonic applications is rarely explored. Here we demonstrate microwave emission and mode coupling from the resonating spin spiral lattice in a Cu₂OSeO₃/Pt/NiFe heterostructure. We use time-resolved resonant elastic X-ray scattering to visualize the exact vectorial spin precession modes from the two magnetic species in real time. Our results show that the ferromagnetic NiFe layer dynamically captures the excitation modes of the conical order in helimagnet Cu₂OSeO₃. The off-resonance NiFe spin precession is phase locked to the helimagnet with a fixed offset, thereby presenting distinct chiral dynamics. This demonstrates that the magnons produced in the process—referred to as helimagnons—can wirelessly transmit spin information at gigahertz frequencies, opening new avenues for on-chip microwave magnonics.

Abstract:

Topological insulators (TIs) have drawn considerable attention for next generation high sensitivity, high efficiency devices thanks to their unique metallic surface conductivity via their topologically-protected surface states (TSSs). In this study, we utilized near-field nanoimaging and nanoscale spectroscopy in the Terahertz (THz) frequency range to explore the optical response of the surface layer from Bi2Te3 TI flakes. In all cases, we observe a higher near-field optical response from the TI flakes compared to a Si substrate. This contrast increases for more surface sensitive probing, which indicates the presence of a conductive surface state. In addition, we have performed temperature dependent THz nanoscopy and demonstrate a significantly enhanced near-field contrast for the TI flake at a sample temperature of 8.9 K compared to the Si substrate. This temperature-dependent behavior provides vital insight into the underlying mechanisms behind the observed conductive surface state in TI materials.

Abstract:

<jats:p>In this perspective article, we explore some of the promising spin and topology material platforms (e.g., spins in semiconductors and superconductors, skyrmionic, topological, and two-dimensional materials) being developed for such quantum components as qubits, superconducting memories, sensing, and metrological standards, and discuss their figures of merit. Spin- and topology-related quantum phenomena have several advantages, including high coherence time, topological protection and stability, low error rate, relative ease of engineering and control, and simple initiation and readout. However, the relevant technologies are at different stages of research and development, and here, we discuss their state-of-the-art, potential applications, challenges, and solutions.</jats:p>