No abstract

Magnetic vortices are characterized by the sense of in-plane magnetization circulation and by the polarity of the vortex core. With each having two possible states, there are four possible stable magnetization configurations that can be utilized for a multibit memory cell. Dynamic control of vortex core polarity has been demonstrated using both alternating and pulsed magnetic fields and currents. Here, we show controlled dynamic switching of spin circulation in vortices using nanosecond field pulses by imaging the process with full-field soft X-ray transmission microscopy. The dynamic reversal process is controlled by far-from-equilibrium gyrotropic precession of the vortex core, and the reversal is achieved at significantly reduced field amplitudes when compared with static switching. We further show that both the field pulse amplitude and duration required for efficient circulation reversal can be controlled by appropriate selection of the disk geometry.

Recent years have seen a growing interest in strong coupling between the electromagnetic modes of plasmonic structures and quantum emitters, as a way to generate new quantum optical testbeds and influence chemical dynamics and reactivity. Strong coupling involving bright plasmonic modes has been achieved in the limit of single quantum emitters. Dark plasmonic modes might fare better in some applications due to their longer lifetimes, but are difficult to probe as they are subradiant. Here, we apply electron energy loss (EEL) spectroscopy to demonstrate that a dark plasmonic mode can strongly interact with a small number of quantum emitters. Using quantum dots (QDs) resonant with the dark dipolar mode of plasmonic bowties, we observe a Rabi splitting of up to 160 meV in EEL spectra.Remarkably, the coupling of QDs to the dark mode occurs at the periphery of bowtie gaps, even while the electron beam probes their center.