Extreme terahertz magnon multiplication induced by resonant magnetic pulse pairs

Abstract

Nonlinear interactions of spin-waves and their quanta, magnons, have emerged as prominent candidates for interference-based technology, ranging from quantum transduction to antiferromagnetic spintronics. Yet magnon multiplication in the terahertz (THz) spectral region represents a major challenge. Intense, resonant magnetic fields from THz pulse-pairs with controllable phases and amplitudes enable high order THz magnon multiplication, distinct from non-resonant nonlinearities such as the high harmonic generation by below-band gap electric fields. Here, we demonstrate exceptionally high-order THz nonlinear magnonics. It manifests as 7th-order spin-wave-mixing and 6th harmonic magnon generation in an antiferromagnetic orthoferrite. We use THz two-dimensional coherent spectroscopy to achieve high-sensitivity detection of nonlinear magnon interactions up to six-magnon quanta in strongly-driven many-magnon correlated states. The high-order magnon multiplication, supported by classical and quantum spin simulations, elucidates the significance of four-fold magnetic anisotropy and Dzyaloshinskii-Moriya symmetry breaking. Moreover, our results shed light on the potential quantum fluctuation properties inherent in nonlinear magnons.

Two-dimensional coherent spectrum of high-spin models via a quantum computing approach

“…Through the application of a susceptibility expansion, we show that the peaks in two-dimensional (2D) frequency space arise from transitions between different eigenstates of the unperturbed Hamiltonian. Finally, we compute the 2DCS spectrum for a two-site spin-s = 5/2 model to compare it with the results of a 2DCS experiment performed on a rare-earth orthoferrite system [40]. The observed strength of the magnonic high-harmonic generation signals in the simulated 2DCS spectra of the quantum high-spin model agrees well with the experiment, in contrast to simulations based on the corresponding mean-field model.…”

“…In figure 10(b) we also show the result of the corresponding mean-field simulation, which is discussed in more detail in appendix C. The high harmonic generation peaks are much weaker compared to the result of the full quantum spin model. Finally, we compare the simulation results with THz 2DCS measurement performed on a rare-earth orthoferrite a-cut Sm 0.4 Er 0.6 FeO 3 sample at room temperature [40], where the system shows canted antiferromagnetic order with a small net magnetization along c-axis [91]. The sample is excited by two collinear THz magnetic pulses polarized parallel to sample c-axis.…”

“…In this section, we study 2DCS of a two-site spin-s = 5/2 model and compare with the results of a 2DCS experiment performed on a rare-earth orthoferrite material [40]. In the simulations we use an antiferromagnetic exchange interaction of J = 1 in the Hamiltonian (1).…”

“…2DCS has also been discussed theoretically as a powerful probe of observing fractionalization, decoherence, and wavefunction properties in quantum spin liquids [27][28][29][30][31], low-dimensional magnets [32][33][34][35][36][37], and random magnets [38]. It has been experimentally demonstrated that THz pulses enable the detection [39,40] and coherent control [41] of collective excitations in the spin degrees of freedom, with their quanta referred to as magnons [42]. Simulating such experiments is crucial for interpreting experimental results and ultimately understanding the physical properties of the studied quantum materials.…”