PCSI2026 Session PCSI-SuA: Exotic Forms of Magnetism

Magnon-based hybrid quantum systems are promising candidates for quantum interconnects and quantum sensors, and they offer a rich platform for exploring nonlinear magnonics and cavity–photon interactions. Two-dimensional (2D) van der Waals magnets provide a compact, atomically flat geometry that can be easily integrated into existing quantum circuits, such as superconducting resonators and qubits. Among various 2D magnets, the magnetic semiconductor CrSBr is particularly unique due to its strong spin–exciton [1, 2], spin–lattice [3], and magnon–exciton [4] interactions. In this presentation, I will first discuss magnon-exciton coupling despite their energetical mismatch by orders of magnitude. I will then discuss our recent work demonstrating coherent coupling between antiferromagnetic magnons in CrSBr and microwave photons in a niobium-based-on-chip resonator [5]. This work demonstrates the first step toward integrating layered van der Waals 2D magnets into superconducting microwave circuits, with full access for both microwave and optical probing. Finally, I will discuss how these properties of magnetic semiconductors can be harnessed for spintronic devices and quantum information science.

[1]Wilson, Nathan P., et al. "Interlayer electronic coupling on demand in a 2D magnetic semiconductor." Nature Materials 20.12 (2021): 1657-1662.

[2]Brennan, Nicholas J., et al. "Important elements of spin-exciton and magnon-exciton coupling." ACS Physical Chemistry Au 4.4 (2024): 322-327.

[3]Bae, YounJue, et al. "Transient magnetoelastic coupling in CrSBr." Physical Review B 109.10 (2024): 104401.

[4]Bae, YounJue, et al. "Exciton-coupled coherent magnons in a 2D semiconductor." Nature 609.7926 (2022): 282-286.

[5]Tang, J., Singh, A., Brennan, N., Chica, D., Li, Y., Roy, X., Rana, F., Bae, Y.J., Coherent Magnon-Photon Coupling in the Magnetic Semiconductor, 2025, Nano Lett., 25, (2025),10912-10918.

Pulsed magnetic fields provide access to extreme field regimes that are essential for probing quantum phenomena and characterizing complex material behaviors. However, their rapid field ramping introduces substantial measurement challenges, particularly the emergence of large Faraday-induced voltages in electrical transport setups. These unwanted voltages, arising from thetime derivative of themagneticflux, can exceed the intrinsicsample signal by ordersof magnitude and result in misleading asymmetries between the up-sweep and down-sweep of the magnetic field. This artifact not only distorts critical features such as quantum oscillations and resistive transitions but also complicates post-experimental analysis. To address this issue, we developed a Python-based software tool equipped with a graphical user interface(GUI) using the Tkinter library. The program enables users to automatically correct for the Faraday-induced voltage component by leveraging the inherentant isymmetry of the induced sign al between rising and falling field sweeps. It applies a least-squares fitting algorithm to extract normalization coefficients (Aₓand Aᵧ) that best describe the proportional contribution of the induced signal in each voltage channel.These coefficients are then used to reconstruct and subtract the unwanted induced voltage component, yielding clean, symmetrized transport data. The GUI design prioritizes accessibility, allowing experimentalists with no programming experience to process their data through a point-and-click interface. Applied to real datasets from pulsed high-field measurements, the tool demonstrated excellent performance in recovering the true voltage response of materials, reducing up/down-sweep discrepancies to within noise levels. By removing the inductive artifact, the program clarifies transport signatures, improves interpretability, and enables consistent analysis across datasets.This tool significantly enhances the workflow efficiency and measurement fidelity for condensed matter researchers utilizing pulsed field environments.

Frustrated magnets host unconventional states stabilized by degeneracy and entropy, from spin ice [1] to quantum spin liquids [2] and pyrochlore oxides [3]. Pyrochlore iridates R₂Ir₂O₇ (R = Dy, Ho) provide a platform with tunable d-f exchange interactions and multiple frustrated phases [3,4]. In these systems, competing interactions suppress long-range order, yielding emergent quasiparticles such as magnetic monopoles [1].

Using Monte Carlo simulations, we map the thermodynamic phase diagram, identifying the 2-in–2-out (2I2O) spin ice, fragmented 3-in–1-out/1-in–3-out (3I1O/1I3O) [4], and all-in–all-out (AIAO) ground states [5]. In this talk, we will investigate the two finite-temperature enhanced-entropy (EE) phases near phase boundaries, characterized by high entropy, strong susceptibility, and mixed spin configurations. These phases are found to be stabilized by entropy-driven free-energy minimization, with distinct behavior of specific heat capacity decoupling from susceptibility serving as key signatures [5] (Fig. 1 in PDF). These EE states define a new class of entropy-stabilized magnetic phases, underscoring the role of frustration in finite-temperature correlated states and offering pathways for entropy-based material design.

[1] A. P. Ramirez, A. Hayashi, R. J. Cava, R. Siddharthan, & B. S. Shastry, Nature 399, 333 (1999).

[2] C. Broholm, R. J. Cava, S. A. Kivelson, D. G. Nocera, M. R. Norman, and T. Senthil, Science 367, 263–273 (2020).
[3] J. S. Gardner, M. J. P. Gingras, and J. E. Greedan, Rev. Mod. Phys. 82, 53 (2010).
[4] E. Lefrancois, V. Cathelin, E. Lhotel, J. Robert, P. Lejay, C.V. Colin, B. Canals, F. Damay, J. Ollivier, B. Fak, L. C. Chapon, R. Ballou, and V. Simonet, Nat. Commun. 8, 209 (2017).

[5] P. Timsina, A. Chappa, D. Alyones, I. Vasiliev, and L. Miao, arXiv:2505.13352 (submitted: PRB, 2025).

⁺ Author for correspondence: lmiao@nmsu.edu