Regensburg 2025 – scientific programme
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SYES: Symposium Electronic Structure Theory for Quantum Technology: From Complex Magnetism to Topological Superconductors and Spintronics
SYES 1: Electronic Structure Theory for Quantum Technology
SYES 1.3: Invited Talk
Friday, March 21, 2025, 10:30–11:00, H1
First-principles study and mesoscopic modeling of two-dimensional spin and orbital fluctuations in FeSe — •Myrta Grüning1,2, Abyay Ghosh1, and Piotr Chudzinski1,3 — 1Centre for Quantum Materials and Technologies, Queen's University Belfast, Belfast, Northern Ireland (UK) — 2European Theoretical Spectroscopy Facility — 3Institute of Fundamental Technological Research, Polish Academy of Sciences, Warsaw, Poland
FeSe is the simplest quasi-two-dimensional iron chalcogenide superconductor, yet its phase diagram exhibits exotic phases like superconductivity, spin density wave, and nematicity, which are intensely studied in condensed matter physics. Understanding the interaction of orbital and spin degrees of freedom is key to explaining FeSe's diverse phases. Using density-functional theory within the generalized gradient approximation, we calculated the structural, electronic, and magnetic properties of FeSe in its tetragonal phase. First, we explored how the d-band bandwidths at the Fermi energy evolve with corrections and long-range magnetic orders. Introducing striped or staggered dimer antiferromagnetic order significantly reduced the bandwidth overestimation seen at the generalized gradient approximation level, aligning more closely with experimental data. Next, we examined the magnetic formation energy for ferromagnetic and antiferromagnetic orders, under pressures up to 6 GPa and derived bilinear and biquadratic spin-exchange energies. We uncovered non-trivial spin-exchange behavior dependent on magnetization and proposed a field-theory model linking this to strong two-dimensional spin-orbital fluctuations.
Keywords: Electronic structure; First-principles calculations; Frustrated magnetism; Vortices in field theory; Iron-based superconductors