TopMagIc: Topological Magneto-Insulatronics

• Applicant: Dr. Alexander Mook
• Subject Area: Theoretical Condensed Matter Physics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 504261060

In the TopMagIc project, we will lay the theoretical foundations of topologically protected magnetic excitations in magnetic insulators to facilitate the development of low-energy technologies utilizing robust magnetic signals in insulators. At the heart of TopMagIc are topological magnon insulators that support magnonic chiral edge states, similar to quantum Hall edge states. As chiral edge magnons lack Joule heating and are immune to back-scattering, they are ideal for meeting the grand challenge of developing technologies with minimal environmental impact. TopMagIc comprises five main objectives that follow a strategy to comprehensively study the topology of magnetic excitations, with a strong emphasis on fundamental questions. (1) Our goal will be to quantify the stability of topological chiral edge magnons in the collective environment of the solid state. We will cover the nonlinearities of the magnetization dynamics itself (magnon-magnon interactions) and those caused by the interactions between the magnetic and lattice subsystem (magnon-phonon interaction). We are seeking to understand how to engineer chiral edge magnons to be stable against nonlinearities. (2) We will identify the qualitative impact of particle-number nonconserving many-body interactions on quasiparticle topology. This open issue in the field of quantum condensed matter is especially relevant to magnons because they realize quantum systems without particle-number conservation. The goal is to demonstrate symmetry-breaking effects of nonconserving interactions, predict resulting transport phenomena, and study magnon topology under strong pumping.(3) We aim to reveal quantum effects in magnon topology that go beyond the semiclassical magnetization dynamics by focussing on many-magnon excitations and spin-quadrupolar order in quantum magnets. Our goal is to bring quantum magnets into the fold of potential platforms of topological spin excitations. (4) To facilitate the experimental detection of chiral edge magnons, we will predict their unique experimental signatures. Besides developing the theory of magnonic quantum geometry, we will, for example, focus on magnetoelectric responses of topological magnons, such as a topological edge polarization.(5) We will explore how to engineer phases with topological magnons. For that, we will follow several routes by analyzing heterostructures of magnetic materials, by developing the theory of topological magnon-light hybrids in cavities, and by exploring non-Hermitian topological functionalities in pumped magnetic systems.

• DFG Programme: Independent Junior Research Groups