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In magnetically ordered systems, fluctuations on top of the ordered state in the form of magnons can induce effective interactions. These magnon-mediated interactions may act to stabilise exotic phases of matter, and also significantly contribute to non-equilibrium responses. I will discuss two recent examples. Numerical results provide evidence for the existence of a partially disordered ground state in the antiferromagnetic stuffed honeycomb lattice, in which collinearly ordered moments coexist with an only short-range correlated subsystem. I show how magnons in the ordered honeycomb system mediate interactions among the central spins and derive an effective model. Fluctuations near the transition between two competing ground states of the model are conjectured to lead to a quantum disordered ground state. I will further discuss how magnon interactions are crucial for the optical generation of coherent magnons in easy-plane antiferromagnets, with a particular focus on the spin-orbit Mott insulator Sr2IrO4. Here, laser fields which directly couple to the local moments induce effective fields which drive a low-energy magnon, giving rise to a finite out-of-plane magnetization. The subsequent dynamics can be probed using a pump-probe protocol.

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Urban Seifert, TU Dresden
Seminar Room 0.03, ETP
Contact: Simon Trebst