Advancing Functional Renormalization for Frustrated Quantum Spin Systems

• Applicant: Dr. Björn Sbierski
• Subject Area: Theoretical Condensed Matter Physics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 524270816

Quantum spin systems continue to be a thriving research topic in modern condensed matter physics. On the one hand, this is due to recent experimental advances in the field of solid state quantum magnets as well as in novel engineered systems like twisted bi-layer Moiré materials or Rydberg atom arrays. On the other hand, there is a steady evolution of theoretical and in particular computational techniques that apply to frustrated and even three-dimensional quantum spin Hamiltonians, one of them being the functional renormalization group (fRG). The established fRG approach for spin systems builds on the long history of fRG for fermionic systems by first expressing each spin through auxiliary pseudo-fermions. However, a recently suggested spin-fRG approach working directly with spin operators promises a dramatically increased efficiency and applicability to new phenomena in quantum magnetism like the valence bond solid or the chiral spin liquid. We propose to advance the spin-fRG by rigorous numerical implementation building on our extensive experience with the pseudo-fermion fRG. We present a work program that balances methodological aspects with applications catering to state-of-the-art problems like the low-temperature physics of the Heisenberg pyrochlore model, prediction of magnetization plateaus or the modeling of recent Rydberg array quantum simulation results.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Jan von Delft