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1. A puzzling insensitivity of magnon spin diffusion to the presence of 180-degree domain walls

   https://doi.org/10.1038/s41467-023-38095-3  

   Li, Ruofan; Riddiford, Lauren J.; Chai, Yahong; Dai, Minyi; Zhong, Hai; Li, Bo; Li, Peng; Yi, Di; Zhang, Yuejie; Broadway, David A.; et al (December 2023, Nature Communications)

   Abstract We present room-temperature measurements of magnon spin diffusion in epitaxial ferrimagnetic insulator MgAl 0.5 Fe 1.5 O 4 (MAFO) thin films near zero applied magnetic field where the sample forms a multi-domain state. Due to a weak uniaxial magnetic anisotropy, the domains are separated primarily by 180° domain walls. We find, surprisingly, that the presence of the domain walls has very little effect on the spin diffusion – nonlocal spin transport signals in the multi-domain state retain at least 95% of the maximum signal strength measured for the spatially-uniform magnetic state, over distances at least five times the typical domain size. This result is in conflict with simple models of interactions between magnons and static domain walls, which predict that the spin polarization carried by the magnons reverses upon passage through a 180° domain wall. 

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2. Investigation of the monopole magneto-chemical potential in spin ices using capacitive torque magnetometry

   https://doi.org/10.1038/s41467-022-31297-1  

   Anand, Naween; Barry, Kevin; Neu, Jennifer N.; Graf, David E.; Huang, Qing; Zhou, Haidong; Siegrist, Theo; Changlani, Hitesh J.; Beekman, Christianne (December 2022, Nature Communications)

   Abstract The single-ion anisotropy and magnetic interactions in spin-ice systems give rise to unusual non-collinear spin textures, such as Pauling states and magnetic monopoles. The effective spin correlation strength ( J e f f ) determines the relative energies of the different spin-ice states. With this work, we display the capability of capacitive torque magnetometry in characterizing the magneto-chemical potential associated with monopole formation. We build a magnetic phase diagram of Ho 2 Ti 2 O 7 , and show that the magneto-chemical potential depends on the spin sublattice ( α or β ), i.e., the Pauling state, involved in the transition. Monte Carlo simulations using the dipolar-spin-ice Hamiltonian support our findings of a sublattice-dependent magneto-chemical potential, but the model underestimates the J e f f for the β -sublattice. Additional simulations, including next-nearest neighbor interactions ( J 2 ), show that long-range exchange terms in the Hamiltonian are needed to describe the measurements. This demonstrates that torque magnetometry provides a sensitive test for J e f f and the spin-spin interactions that contribute to it. 

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3. Spin excitations and dynamics in 2D magnets: An overview of magnons and magnetic skyrmions

   https://doi.org/10.1016/j.pquantelec.2025.100564  

   Wu, Yingying; Balicas, Luis; Cheng, Ran; Zhang, Xiao-Xiao (April 2025, Progress in Quantum Electronics)

   van der Waals magnetic materials open up exciting possibilities to investigate fundamental spin properties in low-dimensional systems and to build compact functional spintronic structures. This review focuses on the recent progress in two-dimensional(2D) magnets that explore beyond the homogenous magnetically-ordered state, including magnons (spin waves), magnetic skyrmions, and complex magnetic domains. Properties of these spin and topology excitations in 2D magnets provide insights into spin-orbit interactions and other forms of coupling between electrons, phonons, and spin-dependent excitations. Such spin-based quasiparticles can also serve as information carriers for next-generation high-speed computing elements. We will first lay out the general theoretical basis of dynamical responses in magnetic systems, followed by detailed descriptions of experimental progress in magnons and spin textures (including magnetic domains and skyrmions). Discussion on the experimental techniques and future perspectives are also included. 

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4. Comb Tensor Networks

   Chepiga, Natalia; White, Steven R (June 2019, Physical review)

   In this paper we propose a special type of a tree tensor network that has the geometry of a comb—a one-dimensional (1D) backbone with finite 1D teeth projecting out from it. This tensor network is designed to provide an effective description of higher-dimensional objects with special limited interactions or, alternatively, one-dimensional systems composed of complicated zero-dimensional objects. We provide details on the best numerical procedures for the proposed network, including an algorithm for variational optimization of the wave function as a comb tensor network and the transformation of the comb into a matrix product state. We compare the complexity of using a comb versus alternative matrix product state representations using density matrix renormalization group algorithms. As an application, we study a spin-1 Heisenberg model system which has a comb geometry. In the case where the ends of the teeth are terminated by spin-1/2 spins, we find that Haldane edge states of the teeth along the backbone form a critical spin-1/2 chain, whose properties can be tuned by the coupling constant along the backbone. By adding next-nearest-neighbor interactions along the backbone, the comb can be brought into a gapped phase with a long-range dimerization along the backbone. The critical and dimerized phases are separated by a Kosterlitz-Thouless phase transition, the presence of which we confirm numerically. Finally, we show that when the teeth contain an odd number of spins and are not terminated by spin-1/2's, a special type of comb edge states emerge. 

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5. Simulating Meson Scattering on Spin Quantum Simulators

   https://doi.org/10.22331/q-2025-06-17-1773  

   Bennewitz, Elizabeth R; Ware, Brayden; Schuckert, Alexander; Lerose, Alessio; Surace, Federica M; Belyansky, Ron; Morong, William; Luo, De; De, Arinjoy; Collins, Kate S; et al (June 2025, Quantum)

   Studying high-energy collisions of composite particles, such as hadrons and nuclei, is an outstanding goal for quantum simulators. However, preparation of hadronic wave packets has posed a significant challenge, due to the complexity of hadrons and the precise structure of wave packets. This has limited demonstrations of hadron scattering on quantum simulators to date. Observations of confinement and composite excitations in quantum spin systems have opened up the possibility to explore scattering dynamics in spin models. In this article, we develop two methods to create entangled spin states corresponding to wave packets of composite particles in analog quantum simulators of Ising spin Hamiltonians. One wave-packet preparation method uses the blockade effect enabled by beyond-nearest-neighbor Ising spin interactions. The other method utilizes a quantum-bus-mediated exchange, such as the native spin-phonon coupling in trapped-ion arrays. With a focus on trapped-ion simulators, we numerically benchmark both methods and show that high-fidelity wave packets can be achieved in near-term experiments. We numerically study scattering of wave packets for experimentally realizable parameters in the Ising model and find inelastic-scattering regimes, corresponding to particle production in the scattering event, with prominent and distinct experimental signals. Our proposal, therefore, demonstrates the potential of observing inelastic scattering in near-term quantum simulators. 

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