Emergent Spin Phenomena

Phonon chirality & angular momentum

Phonons are more than passive carriers of heat. Our work treats their angular momentum as a dynamical degree of freedom that can shape magnetic and thermal phenomena. We study how symmetry controls phonon chirality, how acoustic waves acquire transverse responses, and how angular momentum is exchanged between lattice vibrations and spins.

We identified both intrinsic and defect-mediated routes to phonon Hall transport in ionic crystals. More recently, we showed that even a symmetric crystal vacuum can host finite angular-momentum fluctuations through coherence between orthogonally polarized modes, and we developed symmetry-consistent descriptions of magnon–phonon hybridization.

Quantum many-body dynamics in solid-state systems

We bring ideas from quantum optics into condensed matter by coupling ensembles of solid-state spin defects to a shared magnetic reservoir. Correlated emission into that reservoir can mediate long-range qubit interactions and generate collective dynamics, including superradiance, subradiance, spin squeezing, and many-body entanglement.

This framework also turns correlations into a sensing resource. Instead of treating each spin defect as an independent probe, we use the ensemble’s collective relaxation to access spatially correlated noise and detect broken symmetries in quantum materials.

Dissipation-driven magnetic phenomena

Magnetic systems combine tunable interactions, intrinsic nonlinearities, and controllable gain and loss. We use non-Hermitian and open-system approaches to make dissipation part of the physics rather than a correction to it—revealing phenomena that conventional conservative descriptions miss.

Our work established non-Hermitian topological phases in spin-torque oscillator arrays, connected exceptional points to nonlinear dynamical phase transitions, and identified how inversion breaking and nonlocal damping produce magnetic skin effects. Current public results extend this program to transient topology, metastability, and self-organized nonreciprocal phases.

Emergent effects in magnetic systems

We explore how symmetry, driving, and frustration generate magnetic behavior with no simple static counterpart. One example is our ongoing theory–experiment collaboration on Floquet engineering in magnonic systems. Here, periodic driving creates synthetic dimensions for magnons and enables interactions that are difficult—or impossible—to realize in static devices. Our recent work demonstrates the experimental realization of a synthetic magnonic lattice and shows how dual-tone modulation can produce asymmetric, nonreciprocal coupling between hybrid-magnonic modes.

At the other end of this landscape, our recent work reveals that equally striking phenomena can emerge in equilibrium. We find that a perfectly collinear altermagnet can support persistent spin-current loops carried by its quantum vacuum. A symmetry-allowed staggered interaction imprints hidden vortex–antivortex structures on magnon correlations, producing currents that circulate in opposite directions around neighboring plaquettes. This reveals a striking form of quantum frustration: gauge-invariant fluxes and loop currents survive even when the classical spin order remains collinear, residing entirely within the magnet’s quantum correlations.