Nonreciprocity and Light-controlled Phenomena in Low-symmetry Antiferromagnets: Neutron and Optical Vortex Beam Studies

Effects lacking symmetry under the exchange of source and detector are called non-reciprocal. They are well-known in optics and electronic transport, but can occur for any (quasi)particles, including neutrons, spin waves etc. Numerous possible applications for these effects are in all-optics computing, quantum cryptography, and spintronics. While the non-reciprocal effects involving magnetic (spin-waves) and mixed (electromagnons) quasiparticles are important for both fundamental and applied science, they are not studied as well as those for photons or electrons. Neutron scattering is an ideal probe for magnetic excitations, capable of measuring their spectra with an unprecedented level of details. A team from Rutgers University and NJIT is engaged in a collaborative effort to understand non-reciprocal effects utilizing neutron scattering, advanced crystal growth, and novel optical spectroscopy utilizing circularly-polarized or vortex optical beams. The Project focuses on studies of antiferromagnetic (AFM) materials that exhibit numerous properties beneficial for prospective electronics applications: they are robust against external fields, display ultrafast dynamics in THz ranges, can sustain spin-current transport with micrometer spin-diffusion lengths, and exhibit strong dynamic magnetoelectricity. In these systems, various combinations of absent inversion, time-reversal, and mirror symmetries leads to non-reciprocal effects revealed, for example, in non-equivalent magnon/electromagnon/phonon spectra for the opposite propagation directions. We will grow high-quality monodomain single crystals crucial for studies of nonreciprocal and magnetoelectric effects. The main experimental tools are unpolarized and polarized neutron scattering, as well as visible, THz and x-ray vortex beam spectroscopy. In addition to the standard neutron methods, this Project involves studies of the effects of in-situ circularly polarized or vortex optical beams (as well as other external stimuli) on magnetism, using neutron scattering techniques as the probe, and the associated development work. The primary goal of the latter is to control of the magnetic nonreciprocity with optical methods. Spectroscopic studies will include utilization of vortex beams, which we recently developed as a new probe of orbital magnetism in matter. Combined neutron and optical studies will reveal the physical mechanisms responsible for the exotic nonreciprocal properties in low-symmetry materials, and help identify prospective quantum materials for novel computational technologies.